Both OECD and Eurostat follow the International Labour Office's definitions of "employed". ILO's definitions can be found in 1982's Resolution concerning statistics of the economically active population, employment, unemployment and underemployment:
(1) The "employed" comprise all persons above a specified age who during a specified brief period, either one week or one day, were in the following categories:
(a) "paid employment":
(a1) "at work": persons who during the reference period performed some work for wage or salary, in cash or in kind;
(a2) "with a job but not at work": persons who, having already worked in their present job, were temporarily not at work during the reference period and had a formal attachment to their job.
This formal job attachment should be determined in the light of national circumstances, according to one or more of the following criteria:
(i) the continued receipt of wage or salary;
(ii) an assurance of return to work following the end of the contingency, or an agreement as to the date of return;
(iii) the elapsed duration of absence from the job which, wherever relevant, may be that duration for which workers can receive compensation benefits without obligations to accept other jobs;
(b1) "at work": persons who during the reference period performed some work for profit or family gain, in cash or in kind;
(b2) "with an enterprise but not at work": persons with an enterprise, which may be a business enterprise, a farm or a service undertaking, who were temporarily not at work during the reference period for any specific reason.
(2) For operational purposes, the notion of "some work" may be interpreted as work for at least one hour.
(3) Persons temporarily not at work because of illness or injury, holiday or vacation, strike or lockout, educational or training leave, maternity or parental leave, reduction in economic activity, temporary disorganisation or suspension of work due to such reasons as bad weather, mechanical or electrical breakdown, or shortage of raw materials or fuels, or other temporary absence with or without leave should be considered as in paid employment provided they had a formal job attachment.
(4) Employers, own account workers and members of producers’ co-operatives should be considered as in self employment and classified as “at work" or "not at work", as the case may be.
(5) Unpaid family workers at work should be considered as in self-employment irrespective of the number of hours worked during the reference period. Countries which prefer for special reasons to set a minimum time criterion for the inclusion of unpaid family workers among the employed should identify and separately classify those who worked less than the prescribed time.
(6) Persons engaged in the production of economic goods and services for own and household consumption should be considered as in self-employment if such production comprises an important contribution to the total consumption of the household.
(7) Apprentices who received pay in cash or in kind should be considered in paid employment and classified as "at work" or "not at work" on the same basis as other persons in paid employment.
(8) Students, homemakers and others mainly engaged in non-economic activities during the reference period, who at the same time were in paid employment or self-employment as defined in subparagraph (1) above should be considered as employed on the same basis as other categories of employed persons and be identified separately, where possible.
(9) Members of the armed forces should be included among persons in paid employment. The armed forces should include both the regular and the temporary members as specified in the most recent revision of the International Standard Classification of Occupations (ISCO).
Disabled people who satisfy the above criteria are considered employed, and those that do not are considered inactive and not part of the labour force:
12. (1) The "population not currently active", or, equivalently, persons not in the labour force, comprises all persons who were not employed or unemployed during the brief reference period and hence not currently active because of (a) attendance at educational institutions, (b) engagement in household duties, (c) retirement or old age, or (d) other reasons such as infirmity or disablement, which may be specified.
35. (2) The population of working age, with the exception of the disabled who do not work, and also the population not of working age, are included as labour resources. The balance sheet of labour resources may be broken down separately according to sex, identifying persons employed in subsidiary farming and in house work, disabled persons of working age but who do not work and persons not of working age.
All of OECD's definitions are available online on its Glossary of Statistical Terms.