An .mp3 file is simple file type that is commonly used for audio and sound files. Just as a photo can saved as a .jpeg or .png or .tiff format, audio files can be saved as a .mp3 file and also many other file formats.
Mp3 files became popular in early days of the internet because they were much smaller file sizes. Due to the high compression algorithm used they allowed a good balance between audio quality and file size.
Other audio file formats that you may come across include. .wav .aiff. These are almost always also higher sound quality but also much higher file sizes.
