1. An MPEG standard used especially for digitally transmitting music over the Internet.
2. A file containing a song or other audio data that is encoded using this standard: The band released its latest single as an MP3 on the Internet.

[From MP(EG-1 layer) 3.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.