XP

• Cross-platform ("X" looks like a cross and is often used to replace this word or its synonyms in abbreviations).
• eXtreme Programming.
• Experience points in a role-playing game or in Everything2.
• 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. First two letters in Christ in Greek, therefore symbolic of Christianity. See Labarum.
• 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) completes the process.
• A two-character emoticon representative of a sick or dying person.