Although it is comes from the same plant, white pepper differs from the black in being harvested later, more fully ripened, after which the outer shells of the berries are removed by soaking in water. White pepper is slightly less pungent than the black variety, but tastes otherwise the same. Cooks generally prefer it for use in white sauces and other dishes where the speckled appearance imparted to dishes by black pepper is not thought desirable.
The word ‘pepper’ incidentally, is of Sanskrit origin (pippali, actually the name for long pepper), and has come down to English speakers via the Latin piper. It is interesting to reflect that, before Columbus discovered America, the now-ubiquitous chili was unknown in Asia; pepper was the hottest thing we had!