ATX = the standard for motherboards and cases.
A micro ATX or uATX case can generally only hold micro ATX (uATX) motherboards
A mid ATX or Full tower ATX can hold Micro or ATX boards.
A few cases, generally full tower/super full tower (Corsair Obsidian/Mountain Mods cases/Lian Li super full tower cases) can support eATX motherboards (Extended ATX), though these are few and far between, they are for the people with more money than sense, or home servers