Crowdsourcing is a popular concept that harnesses the wisdom of crowds to solve a problem. This communal wisdom is especially popular online where we vote, rate, and assess content. James Surowiecki published a book called The Wisdom of Crowds on this subject (I haven't read it).
Many famous demonstrations involve a large audience guessing the number of jellybeans in a jar and having the guesses averaged. There have been interesting discussions about how it works, how it fails, and how it could have saved us from the financial crisis.
The answer to the previous meta is crowds.
Amazon Mechanical Turk (Wikipedia) for an archetypal example.
Netflix Prize for another example.
Crowdsourcing - Controversy at Wikipedia for a brief discussion of possible issues.