I messed up a little indie and A are basically the same thing. An example for things that are AA are smaller publishers and developers that still have a decent monetary backing like Devolver Digital, Warhorse studios, Obsidian (moreso when they were contracting out to larger developers like Bethesda but also with their own titles),Bohemia Interactive, platinum games (who make Nier). Essentially lower budget, generally less marketing, smaller but still decent team sizes between 50 and 100 people is considered to be AA. Whereas larger companies like rockstar, blizzard, Activision etc are AAA because they have that huge monetary backing of investors, many teams and sub companies that divvy up the work on multiple large scale projects at a time.