I have been thinking about the way that Congress works. I think that when Congress votes on things, it is an election but only a hundred or a few hundred people are invited to vote on it. Would Congress voting on a bill be considered an election?
No, because an election is, strictly considered, a vote for a person to fill an office. So when Congress has a vote for leadership, yes that's an election, but votes on bills, procedural matters etc. are not elections. See https://en.wiktionary.org/wiki/election
It's worth noting that any questions of policy that are poised to the general electorate are also not elections. The most common term is referendum, although ballot initiative and proposition are also used.