I often see the term "funnel" used in describing adventures or campaigns, but it's not clear to me what it actually means. An example of this kind of use is this blog post talking about playing a "funnel". It doesn't explain what a funnel is, just assumes the reader knows:
I've run DCC RPG funnels. I've even run DCC funnels using the Swords & Wizardry rules. Heck, I ran a short lived DCC RPG campaign and some side arcs.
Saturday night was my first chance to play the DCC RPG, funnel or otherwise, from the player's side of the table, and it was good.
Can someone please provide a description of what it is and how it works in RPGs?