Today, fifty years ago – April 11, 1963 – Pope John XXIII released his encyclical Pacem in Terris, in which the term "subsidiarity" was used (in its modern meaning) for the first time.
A text copy can be found here; see section 140 for the term. But the idea is older, and so is the original term - and if you want further details, please check out the book Subsidiarity, available here.
Note, however, that our own special celebration occurs annually on March 2, which is the "birthday" of Subsidiarity, the day in 2000 when our system went live.
Subsidiarity is the common-sense principle of order and right relation between members and groups of a human social group, or, by extension, any system of cooperating entities.
