V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

MP3
       MPEG audio layer 3 (MPEG, audio, IIS, ISO)


The Free On-line Dictionary of Computing (30 December 2018):

MPEG-1 audio layer 3
MP3
MPEG-1 layer 3

    (MP3) A digital audio compression
   algorithm that acheives a compression factor of about twelve
   while preserving sound quality.  It does this by optimising
   the compression according to the range of sound that people
   can actually hear.  MP3 is currently (July 1999) the most
   powerful algorithm in a series of audio encoding standards
   developed under the sponsorship of the Moving Picture Experts
   Group (MPEG) and formalised by the International Organization
   for Standardization (ISO).

   MP3 is very different from Layer 2, using an additional MDCT
   layer to increase frequency resolution.  Its scale factor
   groups are more optimised for the human ear, and it uses
   nonlinear sample quantisation and Huffman coding.

   MP3 files (filename extension ".mp3") can be downloaded from
   many websites and can be played using software available for
   most operating systems (also downloadable), e.g. Winamp for
   PC, MacAmp for Macintosh, and mpeg123 for Unix.

   MP3 files are usually downloaded completely before playing but
   streaming MP3 is also possible.  A program called a "ripper"
   can be used to copy a selection from a music CD onto your
   hard disk and another program called an encoder can convert
   it to an MP3 file.

   (2001-12-04)