A hog is a pig that's kept on a farm. You can also use the word as a verb, like when you act like a greedy hog. Try not to hog the pie, and stick to your allotted portion.
Though the primary definition of a hog is "domesticated pig," it sometimes refers to wild swine, including feral pigs and warthogs. Hogs are fairly intelligent and social animals, and some of their tendencies are dog-like, including wagging their tails to express pleasure. If your brother shoves cake in his mouth, you might call him a hog, or say, "Hey, don't hog the cake!" Hog originally referred to a one year old pig, but also a horse or sheep of a similar age. "Huckleberry Finn" contains the first known use of hog as a verb meaning "consume greedily."