Pepper is the fermented, dried, unripe fruit of some members of genus piper, especially p. nigrum, the peppercorn tree. They were commonly traded on the Silk Road for their high value to weight ratio. Pepper prices dropped dramatically in Europe after Vasco da Gama reached India at the end of the 15th century
Another species is p. longum: long pepper (AKA pipalli), in which the fruits grow smaller and are tightly clustered, and are harvested in these clusters. A long pepper is not very much bigger in diameter than a peppercorn, though it is up to about an inch long, and each one is composed of many corns. Long pepper is less useful for conventional agriculture because it prefers to grow only in forests, not in fields. With the growth of the pepper industry, long pepper's share of the market has declined.
Another member of the genus, p. cubeba, is not commonly called pepper, and is instead known as cubeb.