The MP3 file format has some striking advantages when it comes to audio files. It's the most common and thus widely-supported format for music and other audio files. Many software as well as hardware music players can thus play MP3 files.
They are so-called "lossy" compressed files. This means that their file size is significantly smaller than other audio files. To achieve this, the audio quality is slightly decreased. Most people can hardly hear the difference and are very happy with the quality of MP3 audio.