The pork, usually a loin, is sliced. It is then coated in flour, dipped into beaten eggs, and rolled in breadcrumbs. It is then fried in hot oil. People often use a Japanese Worcester sauce, but some use a vinegar-soy-sauce called ponzu when they eat it.
Tonkatsu originated as a cutlet, and it came to Japan in the 19th century. Now it is known as a Japanese food by most of the world.