A community of practice is a group of people who share a concern or a passion for something they do, and learn how to do it better as they interact regularly.
This definition reflects the fundamentally social nature of human learning. It is very broad. It applies to a street gang, whose members learn how to survive in a hostile world, as well as a group of engineers who learn how to design better devices or a group of civil servants who seek to improve service to citizens.
In all cases, the key elements are:
members are brought together by a learning need they share (whether this shared learning need is explicit or not and whether learning is the motivation for their coming together or a by-product of it)
their collective learning becomes a bond among them over time (experienced in various ways and thus not a source of homogeneity)
their interactions produce resources that affect their practice (whether they engage in actual practice together or separately)
For a more detailed description of a community of practice, see our Introduction to communites of practice