XP

XP may stand for:

Cross-platform ("X" looks like a saltire cross and is often used to replace this word or its synonyms in abbreviations).
eXtreme Programming.
Experience points in a role-playing game.
AMD Athlon XP CPU.
As the Chi Rho ☧, the symbol that the emperor Constantine I saw in the sky before the Battle of the Milvian Bridge in 312. The first two letters of Christ in Greek, therefore symbolic of Christianity. See Labarum, Christogram, Names and titles of Jesus.
Windows XP operating system. The official Microsoft explanation for this name is a derivation from "experience"; another notes that "Cairo" was Microsoft's codename for an object-oriented operating system that would eliminate completely MS-DOS code from Microsoft Windows; Windows XP (chi-rho, in greek letters) completes the process.
A two-character emoticon representative of a sick or dying person, of extreme laughter of a topic where it becomes so humorous that you would make yourself sick. "XP" may also represent a figure squinting while sticking out their tongue. It is also commonly written as "xP".
Xeroderma pigmentosum, a rare genetic disorder.