What is an ID3 tag? ID3 began life as a simple, informal standard to tag MP3 files with information such as artist, album name etc. In effect the tags are “glued” to the music. The standard has grown (some would say over-grown) over the years, so that nowadays you can store all sorts of things (even lyrics or album art) within an MP3 file. (The other compressed format, like WMA or AAC, have similar tags.)
By far the most important ID3 tags are TRACKNUMBER, ARTIST, ALBUM, TITLE, DATE (somtimes called YEAR), GENRE and perhaps COMMENT. The rest is nice to have but not really important (and won't normally be filled in automatically by the encoding software anyway).
How does the tag information get into the MP3 file? There are two ways: one is to edit the MP3 file manually; most CD rippers and media packages come with a dialog box or another possibility to edit MP3 tags directly. This is feasible for small, local changes but you wouldn't probably want to fill in the ID3 tags for the thousands of songs that you may, over time, put into your MP3 collection. Fortunately, there is a second way. Most programs that produce MP3 or WMA files can locate the album information (ie most of the ID3 tags needed) on one of a couple of internet-based databases. There is Gracenote, formerly called CDDB (short for CD DataBase), which is a commercial venture and is licensed and supported by many of the big software packages that come with the MP3 players. The other is freedb, which works very similar to CDDB but, as the name implies, is completely free. It is also a user-supported database which means that the tags are not always correct. On the plus side freedb has information about albums the Gracenote guys haven't even heard about.
As long as you use the media software that came with your MP3 player there's nothing much to choose from. It will be configured to run with either of the two main databases (and if that's Gracenote the license fees are already paid for by the manufacturer of your player); changing that may or may not be possible (even if it's possible that's probably not a good idea.) Things are different if you do the ripping, encoding, tagging etc. with your own arrangement of software. Please see MP3 Conversion Process and Tools for the details.
The really important thing about that whole tagging business is that you make sure (and double check) that your ID3 tags are correct. This entails two things: they must be downloaded from either the CDDB or freedb and checked before you actually start the ripping and enconding process. Skim the titles for obvious typos, make sure that artist and album name are correct, check year and genre and perform any changes on the names so that they work and are compatible with the directory structure you have chosen. The comment field is a free-for-all: put there whatever you want.
Second, make sure that the internal ID3 tags and the external information (mostly the folder names and the filenames) are in complete agreement with each other. This allows you to re-create the tags from the path/filenames or vice versa, if disaster ever strucks. There are programs out there to read whole directory trees of MP3/WMA files (with many thousand files) and to put the artist, album and title names back into the tag info fields. Or the other way round… in case you ever mix up the names.
It also pays to get a good ID3 tag editor, over and above what your software package has. I use a very powerful freeware application called MP3Tag (see http://www.mp3tag.de/en/index.html — the site and the software is available in German as well as English). MP3Tag can do very simple things on a per-file basis, but it can also do very completely amazing things on thousands of files at the same time. Highly recommended.
$updated from: ID3 Tags.htxt Sat 18 Jan 2014 13:14:24 thomasl (By Thomas Lauer)$