Yap (yăp, yäp) [key], state (1990 pop. 10,886), c.47 sq mi (121 sq km), in the W Caroline Islands, W Pacific. One of four states comprising the Federated States of Micronesia, the island group was formerly part of the U.S. Trust Territory of the Pacific Islands. Yap is a communications center, the principal cable station of the Pacific and an important radio transmitting point. The Yap Islands consist of five closely grouped islands within a triangular coral reef. Discovered by the Spanish in 1791, Yap was sold to Germany in 1899. It became part of the Japanese-mandated area of the Pacific under the League of Nations in 1920 and fell to U.S. forces in 1945 during World War II. Yap is known for the stone disks used as money by the Micronesian natives.