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MP2  or MPEG-1 Layer 2, is a size-compressed, lossy audio format from which the popular MP3 (MPEG-1 Layer 3) format was developed. MP3 came to predominate in computer and internet applications, as it required a lower bit rate (and hence smaller file size) than MP2 to achieve reasonable quality. However MP2 has greater error-resilience than MP3, and at higher bit rates (256 kbps and above) is often regarded as sounding better. For these reasons it is widely used in broadcasting, and includes a 384 kbps option not available in MP3.
Do not confuse MP2 with MPEG-2, which is a standard for video (and associated audio) encoding, whose audio can be in a number of formats including AC3  and AAC 
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MP2 support in Audacity

MP2 files can be imported into Audacity. In order to export MP2 files from Audacity you must use current Audacity. Only current Audacity or legacy 1.3.4 or later supports the highest 384 kbps export bit rate. In current Audacity bit rates can be chosen at time of exporting the file. Simply click File > Export, choose "MP2 Files" in the "Save as type" dropdown, and click the "Options" button.

Note: every time you export from Audacity as an MP2, MP3 or other lossy audio format, the encoding necessarily degrades some of the original audio quality. If you have an MP2 or MP3 file on which you want to perform simple edits (cut, copy, paste, join, fade or normalize), you may prefer an application that can edit MP2 or MP3 directly without having to decompress then re-encode. MP3 DirectCut  for Windows and Audion  for OS 8, 9 and X are two such applications. For more advanced edits, you must accept any perceptible quality loss from re-encoding your MP2/3 when you export.