When referring to the animal (pig), un cochon is a masculine noun. The word takes on other meanings when it is used to refer to a person (Quel cochon ! = What a pig, i.e., a very sloppy, messy person), it may be either masculine or feminine. Needless to say, it is a pejorative term. It can also be either m/f (un cochon/une cochonne) when referring to a person who is obsessed with sex. http://www.wordreference.com/fren/cochon

Cochon is a pig. Porc is a pork. The difference is that chocon is an animal while porc is a food.