Ficcer X may well like her smutfic to involve, say, furniture, office stationary and pineapples. Or a certain character being tied up. Or for both protagonists to have cat ears (yes, you heard me right). Or wings. If this is so, then she is said to have a kink for these items/scenarios/specifications. Fic that centres around a kink is known as kinkfic.
Ficcers are often shy about revealing their kinks. (Actually, that's a lie. About half of them are. The other half will go around comms shamelessly trying to persuade people to write them tailored kinkfic.) This is the reason for the existence of anonymous kinkmemes.
Any particular kink is only a charge if the protagonist character involved in it would have to be OOC to indulge. Notable exceptions are incest and rape, which must be either actually canonical or extremely well-written and justified to escape being a writing sin in the eyes of the PPC.