MP3 files are audio files. They are files that contain different type of audio that has been recorded.
There are other formats that audio files can be recorded in. Microsoft Recorder saves audio files as .WMA files. These files will play in Microsoft Media Player program and a few other programs but not all audio players
MP3 format audio files will play in any audio player program. They will also play on MP3 player devices that some people carry and use to listen to music, etc.
I am using MP3 files as the format that I record my classes’ lectures in, the sermon devotions I give at church and to record my old vinyl records so I can listen to them on modern devices. By recording the lectures my students can listen again later or if they missed class or are taking online listen to what I taught in the classroom.
MP3 format has been around a long time and is recognized as the standard for recording audio files. If you are recording using MP3 you do have choices on quality vs. size of the file. I generally record at high quality just as I do with my picture files.