XP (Extreme Programming) is a system of practices (you can use the m-w — Extreme programming

"One of the things Ive been trying to do is look for simpler or rules underpinning good or bad design. I think one of the most valuable rules is avoid duplication. "Once and only once" is the Extreme Programming phrase."

"One of the central axioms of extreme programming is the disciplined use of regression testing during stepwise software development."

"Extreme Programming is a discipline of software development with values of simplicity, communication, feedback, and courage. We focus on the roles of customer, manager,and programmer and accord key rights and responsibilities to the people in those roles."

"But you could do extreme programming. In fact, I had a college buddy I did pair programming with. We took a compiler writing class together and studied all that fancy stuff from the dragon book. Then of course the professor announced we would be implementing our own language, called PL/0. After thinking about it a while, we announced that we were going to do our project in BASIC. The professor looked at us like were insane. Nobody else in the class was using BASIC. And you know what? Nobody else in the class finished their compiler either. We not only finished but added I/O extensions, and called it PL 0.5. Thats rapid prototyping."

"Extreme Programming is an “agile methodology” that some people advocate for the high-speed, volatile world of Internet and Web development."

"Extreme Programming is the first popular methodology to view software development as an exercise in coding rather than an exercise in management."