It is in the purest sense a frank, to the point conversation that involves no trying to interpret the "deeper meaning" and involves no advice-giving. There's a code of chivalry that a man's gotta do what a man's gotta do. Rarely does guy talk involve personal relationships except in the most cursory of ways unless one guy is going through some problems and needs some advice. Guy talk NEVER involves talk about what happens in the bedroom or gossip. Guy talk said in the room/bar/dwelling/strip club stays in the room/bar/dwelling/strip club.
Not all humans of the male gender are capable of pure guy talk and by definition, no human of the female gender is capable either (just as no human of the male gender is capable of pure "girl talk"). Some women can come very close, but not being a guy and not understanding what it is to be a man makes it literally impossible for a woman to engage in guy talk in the purest sense.