A "pig" is the animal, "pork" is the meat.
This actually goes back to the mixing of French and Anglo-Saxon words during the Norman Conquest of England. At that time, English acquired a lot of words from Latin-derived French words.
"Pig" is derived from Anglo-Saxon, "Pork" from French and Latin.
There are a number of other such pairs. "Ox" and "steer" and "cow," the animals, are Anglo-Saxon; "beef," the meat of these animals, is from French.