A Community Of Practice is a group of people who are in some sense defined by their task. A group of practitioners involved in a common activity, albeit performing different roles. Here's another, from a page devoted to the topic . At the simplest level, CoPs are small groups of people who've worked together over a period of time and through extensive communication have developed a common sense of purpose and a desire to share work-related knowledge and experience. This is called Legitimate Peripheral Participation .
Reputation plays a central role.
The Social Life of Information , by John Seely Brown and Paul Duguid, is new in 02000.