1. Slang often used for describing Microsoft Windows XP.
2. When referring to a game, XP is also used as an abbreviation in RPGs or MMORPGs for eXPerience. XP is often gained when a player in a game defeats an opponent of similar skill or level. When the player gets enough experience, his or her level will increase.
4. XP or xP is also an emoticon with its tongue sticking out.