Today it means: A process designed, particularly in time-critical situations, to empower everyone in a team, however junior, to efficiently call attention to an error or danger, give useful information, or propose a course of action, with the intent of pooling the team's knowledge and creativity to avoid or minimise any emergency and obtain the best practicable outcome. Full definition →
Coined in 1979 by John Lauber, initially as "cockpit resource management", relating to those on the flight deck of an aircraft, then broadened to "crew resource management" to include the cabin crew, and later genericised to other industries, often with unaltered wording. More at Crew resource management.
Etymology from Wiktionary, CC BY-SA 4.0.