The Latin collegium (pl collegia) does not signify an educational institution, but rather a group of men dedicated to a specific purpose. There were a huge number of collegia in Rome, which ranged from the college of Augurs you mention and the college of pontifices (priests), which were prestigious offices normally held by high-powered, aristocratic politicians, all the way down to something more like a tradesmen's guild for all the craftsmen in a particular business in a particular neighborhood.

u/xenophontheathenian has written about collegia here,although more can always be said.