This article introduces what's iTunes tag, and how you can edit it in iTunes, or using external iTunes tag editor.
What's iTunes Tag?
iTunes tag, also called iTunes ID3 tag, is the metadata or information like artist, album, genre, year and so on. In iTunes, the tags are mainly used to categorize your music, display information for the files, sort the files and be used by Smart Playlist.
iTunes Built-in tag editor
Editing tag in iTunes is very convenient. Directly highlight a song and click once to editing tag one by one. Plus, iTunes also allows you to edit the tag informations with the built-in info editor. To access it, right click on the file you want to edit metadata, and select Get Info (or just press Command + I on keyboard).
Tips: the Grouping field are specially used to group songs for dynamic playlists. For example, you can create a Smart Playlist to generate a list that just contains the songs with "Oldies" grouping information.
Tag Edit Multiple Songs in iTunes
You could also edit tags of multiple songs. It's similar to editing tag of a single file. The difference is to select multiple files before access Get Info command. You can hold down Command or Shift key and click to select multiple files, or use Command + A to select all files.
Tips: If you want to clear an iTunes tag such as comment, simple uncheck the box before comment text field and choose OK to apply to selected files.
External iTunes tag editor
The tags edited iTunes sometimes have not been saved to the original file, so it doesn't work with other programs. Moreover, it's not as powerful as some external tag editors. Here comes the other tag editors for iTunes. What I recommended here is the free iTunes tag editor called MusicBrainzPicard which uses an album-oriented approach to access the MusicBrainz database to automatically tag your music files correctly.