A peppercorn is the dried berry of the pepper plant. The black peppercorn is most common, while white and green peppercorns are produced from the same plant simply by picking them during different stages of ripeness.
Black peppercorns are produced by picking the berry just before it is ripe. It is dried until it shrivels and turns black. These black peppercorns are then ground to make the black pepper that is commonly used as a seasoning.
White peppercorns are produced from the fully ripened berries, while green peppercorns are produced from the fully unripe berries and are preserved in a brine.