One of the best definitions of a team is:
"A team is a small number of people with complementary skills who are committed to a common purpose, performance goals, and approach for which they are mutually accountable."
(Katzenbach and Smith, 1993: The Wisdom of Teams: Creating the High-performance Organization. Boston: Harvard Business School.)
A slightly better operational definition we use, is
“Our team is a group of individuals who hold each other mutually accountable for a shared outcome”
- what is your definition of a team?