For the purposes of this tutorial, a tag is a piece of information stored inside a music file. Tags primarily provide information about the audio within the music file, but they can also be used for information about other connected items, such as the artist of the audio, information about the release that the recording is featured on and more.
For a piece of audio, typical tags will include the name of the work, its containing release, its position in the containing release, the artist of the work, the year of the release's original release, the audio's genre and more.
Tags are very important because they form the basis of browsing, organising and searching in your music player. When you see album and artist names in your music player, that's the tags you're seeing. So if your music file doesn't have tags, the information in your music player will be incomplete and your music will be harder to find and play!