Cohort
\ˈkoʊhɔrt\
A group of people from a given population that share a common time period for some event (such as birth or retirement).
A birth cohort is a group of people from a given population defined by the time of their birth. For example, the group of men born in the UK in 1930 form a birth cohort (the population is “men born in the UK” and the birth definition is “1930”), whilst the group of men born in the UK over the period 1925 to 1935 also form a (wider) birth cohort (the population is unchanged, but the birth definition is now “1925 to 1935”). The term is often abbreviated to just ‘cohort’; but cohorts can be equally well analysed according to, for example, year of retirement or year of starting employment.