Everyone has come across this term. EXtreme Programming (XP). First thought I had was: Probably this is programming in extreme environment condition, like minus 20 degrees or hanging with your head upside down. I bet that many people had similar concept about XP. In practice eXtreme Programming is a basket of rules, methods and disciplines for Software Planning, Design, Development and Release.
Im not writing as an expert on this subject, just someone who recently introduced XP practices into my developer life.