Actually, there is a track information encoding system defined as part of the music disc encoding standard, but it's incredibly rare to find it being used on a commercial CD. In fact, I don't know that I've ever seen it. Instead, what iTunes is doing is using the CDDB, the CD information database, now known as Gracenote, a Sony Music Corporation service.

What's cool is that the CDs are identified by the track information itself: how many tracks, how long they are, etc. As Sony describes it:

"Using the CD's unique Table of Content (TOC), MusicID can identify CDs released around the world. Even with multiple pressings and release dates, patented fuzzy matching enables accurate recognition."

However the magic works, there are definitely some times that you insert a CD and end up looking at something like this:

Before you enter the information track-by-track from the CD information, select every track while you're still viewing the CD (not its unlabeled copy in your iTunes library) and Cmd-Click:

That's what you want, "Get Track Names".

iTunes will then query the Gracenote media database:

... and not more than a few seconds later, suddenly every track has all the information you need:

If you already made the mistake of importing the tracks before you matched their names, iTunes will now see the CD as new and ask you if you want to import it again!

If you have already imported unlabeled tracks, you can either also import the identified tracks and delete the unidentified ones, or instead of what I just showed you, there's a way you can check for name and track information missing from tracks already in your iTunes library.

Here you can see that I've selected a stack of tracks, then am selecting "Get Track Names" from the "Advanced" menu:

This time it'll ask if you really want to go out onto the network for this information:

Of course you do! Click on "OK" and just a few seconds later all the track info it can find will replace, track-by-track, the unknown tracks in your library. Very useful!