"Extreme" suggests that it has very different from normal, very aggressive, exceeding limits, but in my opinion regular releases, pair programming, unit testing, collaboration with customers are quite normal and acceptable. What does extreme mean?
From the C2 wiki:
"Extreme" means these practices get "turned up" to a much higher "volume" than on traditional projects. XP ignores any other practice (like BigDesignUpFront) that does not appear on the list. The result is stable, productive, and very rapid because the practices support each other the more they are used together without interference. An Extreme project is typically so stable and sedate it can lead to FortyHourWeeks without any schedule slips.
Extreme Programming or 'XP' (nothing at all to do with windows in this case) meant a different approach to the traditional methods of 'requirements - coding - testing - deployment' as separate phases that followed sequentially.
Extreme Programming meant using new Agile approaches that puts the customer at the heart of development.
The work itself emphasizes teamwork to avoid the more traditional 'silo-ing' of areas such as IT, Sales, Marketing, Customer Service, etc.
It uses 5 key areas - communication, simplicity, feedback, respect, and courage.
This was an extremely different approach when the Extreme Programming project was first introduced on March 6th 1996.
Today, nearly 20 years later, with the Agile movement in full-swing it's starting to become the norm in many industries and doing things the older, traditional way, might soon become extreme!