When a big new phenomenon comes around, the idea and the implementations naturally diverge. New ideas attach around the core, attempting to extend or in some cases co-opt the original idea's meaning. Some, like "nanocasting," don't stick. But others may, and after a fashion, people need to step back and arrive at the gestalt of the situation: a complete definition of the landscape evoked by a term.

And so, we come to that moment of collective introspection. Podcasting has to mean something. But what?

In addition to being a topic of discussion within several podcasting hangouts, now comes Microsoft ur-blogger Robert Scoble. He and a colleague are debating what, exactly, can be called a podcast. Can it be video? If not, what if the iPod supports video in the future? Would that change the definition down the road?

Here's my attempt at the unified theory: use "podcast" as an adjective.

If you listen to Staccato, my music show, you'll find that I never refer to it as a podcast, full stop. It's always a show. "Podcast" to me refers to a specific mechanism for transferring the data: namely, the RSS 2.0 <enclosure> element. (The Atom <link> element is also acceptable -- and more flexible.) As long as it's pointed to in an RSS or Atom feed, "podcast" is good enough for me.

Well, almost. You still have to know what the payload is. Is it a podcast talk show? A podcast soundseeing tour? A podcast videoblog? All of the nouns here function without "podcast" as a modifier. It's only when podcast is used by itself that confusion results.

To resolve that confusion, here's what I suggest as the minimum criteria for using "podcast" as a noun:

• Content is delivered via RSS or Atom feed.
• Content is in MP3 format.

In other words, when Rush Limbaugh calls himself "the hottest thing in podcasting," he's wrong. Rush, like the other Premiere Radio hosts, do release MP3s -- but using a proprietary interface. Allowing this kind of thing to be called a "podcast" weakens the brand, because it takes control away from the user. Imagine having to download a different program for each podcast show you subscribe to. It's a nightmare scenario for users. If they get away with co-opting our term of art, we're looking at a vastly different landscape -- one that independent podcasters will easily be shut out of.

What if the document is in another format? That is, what if Microsoft wants to release WMA files rather than MP3s? Well, I would make that clear right on the link: "WMA Podcast". It's a given that MP3 Just Works in all existing podcatching systems. Other formats lead to complexity, and that leads to user confusion, which leads to dissatisfaction, depression, Prozac and death. (Okay, just dissatisfaction. But that's bad enough.) If it's not a given that users will be able to do what they desire with the file, including playing it on the device they have, that should be expressed beforehand.

It seems like a petty thing to be bringing up at this stage, but we have to be clear what we're talking about here, because everyone who learns what a podcast is becomes a potential listener. If they can't trust the term, they'll be turned off before they even turn on. Let's see some consistency in our terms before we lose all control.