(FORTUNE Magazine) – I know this may sound obscure but, dear reader, I simply must tell you about metadata! Metadata presents the biggest challenge the tech industry faces in delivering the ubiquitous, ever present, networked future. Whether it's the seamless integration of data into your cell phone, downloading digital music at home or in your car, or getting your bank and brokerage house to cooperate online, it doesn't work without metadata. In fact, if you understand the value of metadata, you'll know why Bertelsmann's offer to lend $50 million to Napster won't necessarily save Napster.

Metadata is information about information. Let's say you have an MP3 file on your hard disk. The information in that file is the bits that represent the music in a way that allows the computer to play it back accurately. The metadata is the information associated with the file, information that you and the computer want to know: the name of the file, its size, its length, the name of the song, the genre the song belongs to, and so on.

Right now I'm playing Eric Clapton's "After Midnight" in the background while I write this column. That is very cool, because Eric Clapton ranks right up there in my personal hall of fame. It is a pretty good recording of "After Midnight," probably copied from one of Clapton's music CDs. But I got it from Napster, so I don't know where it came from.

Here's the metadata that I do have on the file: I know that the file is 2.7 megabytes big, that it is two minutes and 50 seconds long, and that it was recorded at 128 kilobits per second. I also know the file is named "Eric Clapton--After Midnight."

Here's some of the metadata I don't have on the file, unfortunately: I don't know who published the song, which CD it was recorded from, which music company distributed the CD, or who wrote the lyrics. I know nothing that might help me pay for the rights to listen to the song, if I wanted to pay. I'm also missing any metadata that would tell my computer which genre of music the song belongs to, or any other data that might help it play this song for me at just the right time, given what it might know about my taste in music. And one of the key pieces of metadata that I do have is a mess: Since someone has renamed the file to include both the name of the artist and the track title, the computer can't figure out how to slot the song into the right place on my hard disk, with other music labeled by only artist or song.

I picked this particular file because it has been fully Napsterized. Stolen from a CD, renamed by a user, and never matched up with another source of metadata, it is now just a song in a file. It has no other value to me. But to be totally fair, other MP3 files on my hard drive that have not been Napsterized also lack useful metadata. For instance, my copy of the Beach Boys' "Good Vibrations" correctly identifies the album it was originally on and the year it was published. But that's it.

Anyway, by now you probably get the point: In the music business metadata will be the key to providing a legal system for distributing and selling music as well as useful services to people who want to listen to music. And that's just the music business. The same holds true for all digital media: books, television, movies, magazines, even software itself.

But metadata is important well beyond the media business. For instance, I've been using e-mail for serious business purposes for more than ten years, but I've never figured out a simple way to keep a good digital record of my e-mail messages. The reason: E-mail lacks useful metadata. It has a smattering: The to, from, cc, date, and subject lines are all metadata for the content of the message. But that metadata was designed to help computers route and list the messages, not to help you store, retrieve, and manage them.

Start thinking about the digital world, and you'll begin to see just how important metadata truly is. Have you taken more than 100 pictures with that digital camera you recently bought? You'll discover that there's not much metadata for all those picture files; too bad, because with pictures, the value of metadata is amplified since you want to keep them forever and remember years later why they mattered. Metadata matters in the business-to-business world as well. As more corporate transactions are conducted over the Net, each needs metadata so that companies can track the transaction and analyze its success. It is the basis of accounting for the Digital Age.

The problem, for now, is that metadata is information about information, as obscure a topic as there is. But you should keep an eye out for companies that specialize in metadata. In the music business, for instance, a little company in Berkeley called Gracenote specializes in collecting metadata about CDs. It now has a database of names, artists, track titles, and a bunch of other stuff that allows it to recognize a music CD instantly when it is inserted in the CD-ROM drive of a computer and show you what you are listening to. In the right hands, that could be worth something big. Even if it is nothing more than information about information.

STEWART ALSOP is a partner with New Enterprise Associates, a venture capital firm. Except as noted, neither he nor his partnership has a financial interest in the companies mentioned. He can be reached at alsop_infotech@fortunemail.com. His column may be bookmarked online at www.fortune.com/technology/alsop.