The Mega reference article from the English Wikipedia on 24-Apr-2004
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Mega

Mega (symbol M) is a SI prefix in the SI system of units denoting a factor of 106, i.e. one million; 1,000,000.

For example, a megawatt is 1,000,000 watts = 1,000 kilowatts.

Other common examples of usage:

The prefix "mega" also means "large", coming from a Greek word with that exact meaning. An example of a word with "mega" meaning large is Megalosaurus.