Parties such as those united under the European People's Party tend to tag themselves as "popular" or "people's" parties. Does this term have any ideological value? Or is it just a non-religious synonym for Christian democracy?
As far the EPP goes, it does seem that "people's"/"popular" (actually the German word "volk") was chosen as to seemingly broaden the appeal of the group, although you might as well see the naming as victory of the more conservative Germanic wing over its Romance members. I found practically nothing published on the actual discussions that led to the naming of the EPP, but the broader context has been well documented.
The founding members of EPP (1976) in their original names (some have changed since):
- Flemmish CVP - Christelijke Volkspartij
- Wallon PSC - Parti Social Chrétien
- German CDU - Demokratische Union Deutschlands
- Bavarian CSU - Christlich-Soziale Union in Bayern
- France CDS - Centre des démocrates sociaux
- Ireland Fine Gael - "Family (or Tribe) of the Irish"
- Italy DC - Democrazia Cristiana
- Luxembourg CSV - Chrëschtlech Sozial Vollekspartei (or PCS - Parti populaire chrétien-social in its French name)
- Dutch KVP (Katholieke Volkspartij), CHU (Christelijk-Historische Unie), ARP (Anti-Revolutionaire Partij) participated individually. (The CHU and APR were roughly the Protestant equivalent of the KVP; historically the CHU and ARP were split on the degree of cooperation they would entertain with catholic parties) These three parties would soon enough merge into the Dutch CDA (Christen-Democratisch Appèl).
As you can see "volk" naming was hardly majoritarian, even if you include the Irish. But also clearly the "social" naming was favored in the Romance languages. These latter parties tended to be smaller and less influential in their home country constituencies through. Luxembourg seems to have been the "compromise" as it had both "social" and "volk" its party name...
If you want to dig into the guts of the CDU, it had a history somewhat resembling the Dutch CDA, i.e. when the CDU was formed by merging several parties, those included the Deutschnationale Volkspartei (DNVP) and the Deutsche Volkspartei (DVP). It's more iffy to call the DNVP and DVP Christian democrats, but they included some Christian-tradition appeals in their ideology. (The DNVP had a more völkisch ideology than the DVP which was more liberal.)
If we take KVP as the naming "standard", according to Wikipedia (which frankly seems to me to be overselling this point):
The name Catholic People's Party (Dutch: Katholieke Volkspartij; KVP), must be seen in contrast with the name of its predecessor Roman Catholic State Party. The party no longer uses the name "Roman Catholic", but simply "Catholic", de-emphasising its religious affiliation. It is no longer a state party, but a people's party, emphasising its progressive, democratic nature. The new name emphasises the KVP's progressive, democratic and non-denominational image.
When the EPP was formed, the story goes that there were actually two wings inside it. The German one which was more right-leaning and saw the EPP as the main counterweight to the socialists and communists. And the smaller countries' CD parties (Belgium, Netherlands) which were more inclined to ally themselves with a left-wing party in order to govern. Before 2005, the "grand coalition" didn't have much tradition in Germany, at least at the federal level. On the other hand, going back to the KVP (again according to Wikipedia):
The KVP had a strong centre-left group within its ranks. These supported closer cooperation with the social democratic PvdA. This resulted in several cabinets with the PvdA, but also splits within the party, most notably the formation of the Political Party of Radicals.
The fact that CDU/CSU were not as enthralled/sure of where the EPP was going back then could be seen in how they hedged their bets with their membership in the EDU, which didn't include much CD but rather Conservative parties from other countries, at least when it was formed:
The German parties, which have for some time tightened their links with the Conservatives, would rather see the Christian-Democrats adopt a firmly anti-communist and even anti-socialist line. Parallel to the creation of the EPP, existing contacts were intensified between some C-D and Conservative Parties, and they led to the creation of the European Democratic Union (EDU), which officially saw the light in Salzburg in April 1978. Two members of the EPP - the CDU and the CSU - were among the 10 founding members, the others being the British, Danish, Norwegian, Swedish and Finnish Conservative Parties, the French RPR, the Portuguese Centro Democratico Social and the Austrian Volkspartei. Two more parties from the Nine took part as observers: the Sudtiroler Volkspartei (an Italian regionalist party, [observer] member of the EPP) and the French PR (affiliated to the ELD). Although they had been invited, the Italian DC, the French CDS and the three Benelux C-D parties refused to attend [the EDU].
As for what happened after the EPP became a banner, I suspect, but have no definitive proof that a lot parties have tried to capitalize on the "people" banner. Spain's PP (formed after the EPP) was also a case of a "broad tent" (to borrow a term from US politics), as the PP included conservatives, Christian democrats and even Francoists. After Aznar reshaped the PP's image (as less Francoist), its membership in the EPP became possible; as one book summarizes:
Soon after being elected to succeed Fraga as PP leader in April 1990, José Maria Aznar made contact with the EPP leadership to discuss the necessary steps for sustaining the cooperation, in other words, for joining the EPP. For his part, Aznar would have to overcome internal, right-wing conservative opposition to enter the EPP. Within the EPP, the resistance of the Catalans and Basques in particular was another obstacle: for internal reasons, they opposed entry by the PP. The Italians, Belgians and Dutch, among others, had to be convinced that the Spanish party had undergone a genuine conversion and that the conditions existed for cooperation in a spirit of mutual trust and for a common policy at European level based on Christian Democratic principles.
In the meantime, Wilfried Martens, then still Prime Minister of Belgium, had been elected President of the EPP in May 1990. From the outset he had been a strong advocate of opening up the EPP and actively supported the PP’s admission. The attitude of his own party, the Flemish Christian People’s Party (Christelijke Volkspartij, CVP), was guarded to negative. [...]
As you can see it was again a case of the most left-inclined CD parties (non-German ones) that had most qualms about the Spanish PP joining the EPP.
Interestingly perhaps, none of the Nordic CD parties named themselves with "folk" in the name. On the other hand, Denmark has a Konservative Folkeparti (DKF). It was allowed into the EPP together with other Nordic conservative parties once the Swedish KD (Kristdemokraterna) relented.
Outside of the initial members of the EPP, only Austria's ÖVP (again in the Germanic camp) had a strong C-D ideology as well as "volk" in their name.
The EPP now also includes Slovenian People's Party, Romania's People's Movement Party and the Polish People's Party, but in all three of those countries there's another EPP member that doesn't have "people" in their name and has had more electoral success. (Romania has a National Liberal party as EPP member, Slovenia has a Slovenian Democratic Party as EPP member, and Poland has the Civic Platform party in the EPP). I know little of their ideology, i.e. I don't know exactly how more or less C-D the "popular"-named parties in these countries are compared to their other EPP members.
(If you want to delve on [other] naming similarities, Romania's major EPP member, their National Liberal Party has a name identical to [Germany's] DVP predecessor. And in history repeating itself kinda fashion, some DVP members joined/formed the FPD after the war, itself an [European] ALDE member nowadays... just like splinter groups from Romania's NLP formed the Romanian ALDE--you don't get anymore clear political down-copy of a European party name than that, although amusingly the Romanian ALDE was rather snubbed by its European counterpart.)
As "popular" also suggests "populist" (the "volk" vs "volkish" has a somewhat similar connotational issue, likewise for "national" vs "nationalist"), it's worth also recalling that the EPP has had a stormy relationship with member parties that (perhaps) tacked too much in the direction of the populist or the far right (depending how one defines these terms), in the view of some EPP members. The EPP has had seen open internal strife dealing with the so-called Haider affair, when the Austrian FPO joined the OVP in government (for the first time) around the year 2000:
The question of whether the Austrian People’s Party (which is a member of the EPP) should be sanctioned for its coalition with the FPO proved to be a strong bone of contention among the European mainstream Right. The divisions that emerged inside the EPP largely overlapped with the [...] divisions between national public opinions. Several national delegations, including the French-speaking wing of the Belgian Christian democrats, the French UDF, the Italian PPI, as well as the leader of the Spanish People’s Party, Jose Maria Aznar, asked for an exclusion of the OVP. They argued that its coalition with a far right party broke with the codes of conduct the EPP had committed itself to in its Athens Programme of 1992, including the rejection of nationalism and of all forms of extremism (EPP 1992: 20). This point of view was strongly opposed by the German, Flemish-speaking Belgian, Nordic and British delegations, as well as by Forza Italia, which rejected the idea of a principled condemnation of the OVP/FPO coalition, contending that it had to be judged on its policies. This controversy was only superficially settled with the adoption by the EPP leadership of a report written by three EPP representatives which concluded that the policies of the OVP/FPO coalition were in line with official EU values (Van Velzen et al. 2000); [but] this disagreement has had far-reaching consequences for the party federation.
[...] much of the justification for the sanctions on the part of the EU-14 was based on the definition of the FPO as an ‘extreme-right’ party (a definition which is also used by the EP’s resolution of 3 February). This qualification, however, does not have the same meaning in all countries. In the French or the Belgian discourse, it was taken for granted that the FPO was an ‘extreme-right’ party, which was seen as an equivalent of the French Front National or the Belgian Vlaams Blok. In German-speaking countries, however, the term ‘right-extremism’ has a specific meaning; as Cas Mudde underlines (1996: 230–31), it refers to parties or political forces that reject democratic values and therefore pose a threat to the democratic regime. This explains why the use of the term ‘right-extremism’ in reference to the FPO did not make much sense in Germany or in Austria, where the majority of party officials, even among the Left, define the FPO as a ‘right-wing populist party’ [...]
One could first argue that different countries have historically devised different responses to right-wing extremism. For instance, Kestel and Godmer (2004) distinguish between the ‘German model’ of ‘exclusionary oligopoly’, which implies the absence of any cooperation with right-extremists at all levels of government and the ‘Austrian model’ of ‘inclusive oligopoly’, which includes the ‘pariah party’ in government at regional and federal levels. These differences in terms of national political culture might explain why member parties belonging to the same European party federation could not agree on the Haider issue. For instance, inside the EPP, the French delegation of the UDF contended that the ‘German model’ should have been applied to the FPO, thus projecting on the Austrian case the strategy that French mainstream parties have applied to the Front National since the 1998 regional elections (when some UDF officials were expelled from the party for being elected as presidents of regions with the support of the Front National).
[...] whereas the Christian democratic Italian People’s Party (PPI), a historical member of the EPP, called for an exclusion of the Austrian conservatives [OVP], representatives of Forza Italia strictly opposed it. From this point of view, the Haider affair exposed the growing ideological incoherence of the EPP [...]
So yeah, EPP parties could not agree how much (right-wing) populism is too much, at least in that (OVP/FPO) case. Note that this division didn't have a lot to do with their names though... The EPP seem to have more of an agreement on Fidesz with its (recent) indefinite suspension, for anti-democratic practices. I should also note that the "German model" (that that 2005 paper talks about) is difficult to apply uniformly in Germany anymore, with the rise of the AfD.