What's the origin of the words Pork and Beef?

Fish is from a fish, chicken from a chicken, but beef is from a cow and pork is from a pig, why is that?

From the French boeuf and porc.

After the Norman invasion, French was the language of the court. They used the French word for the animals when serving them as meals. The peasants, who actually raised the animals, used English.

There are other examples, such as venison.

RealityChuck has already answered the OP, but I’ll take this opportunity to bring up this passage from Ivanhoe. Wamba, a jester, is talking to Gurth the swine-herd:

Also …

veal (calf meat)
mutton (sheep meat)
chevon (goat meat)