Macs is the term used for the Macintosh brand of computers. Generally used by people who like to think they are tech wizards because they don't use the "mainstream" PCs.
They often argue that Macs are faster than PCs, but what they usually don't understand that PCs are a large variety of computers that merely run the Windows operating system. For the price you can get a mac for you can get a god-like Windows computer customizable to the max.
Seriously. Stop trying to be tech hipsters. Use a PC.
Macs: Yeah, I use Macs. PCs suck.
PCs: Hey, did you hear about Portal 2? It's great you should really try it.
PCs: So I was right clicking the other day....