a reference work containing short biographical entries on the outstanding persons in a country, industry, profession, etc.: a who's who in automotive engineering.
the outstanding or influential persons in a community, industry, profession, or other group: The who's who of racing will be there.
The outstanding or best-known individuals of a group, as in Tonight's concert features a veritable who's who of musicians. This expression comes from the name of a famous reference work, Who's Who, first published in 1849, which contains biographical sketches of famous individuals and is regularly updated. Its name in turn was based on who is who, that is, the identity of each of a number of persons, a phrase dating from the late 1300s. [Early 1900s]
