Many online sources make the claim that the strange quirk in the English language of having French-derived terms (pork, beef, veal, mutton) for the meat of the animal, and having German-derived terms (pig/swine, cow, calf, sheep) for the animal themselves is due to the Norman conquest.
The claim follows that since the French were the aristocrats and the English were the workers, the aristocratic French word was used to refer to the meat and the working-class English word was used to refer to the animal.
For example, the claim is made by this article:
So, what does all this have to do with cows and pigs? Well, seems that the Anglo’s were made to tend to the livestock for the new Norman gentry. To them, a cow was a cow and a pig was a pig. When their was a big dinner or lavish affair going on, the Anglo serfs were made to tend to the livestock and then deliver it to the kitchens where the Norman cooks and chefs took over planning and serving the meal.
During the reign of William the Conqueror, traditions and language became somewhat mixed as English began to evolve further. For the Norman chefs, the word for cow was pronounced “beuf” which ended up becoming “beef” and pig was generally pronounced as “pauk” which evolved into the present “pork”.
However, this claim is unsourced, and this The Straight Dope article claims that there is no proof that this theory is correct.