The "Zencast" is almost identical to the Podcast, only it refers to playing downloaded "casts" on a Creative Labs mp3 player. Creative Labs coined the term, most likely, in attempt to topple Apple's dominance of modern parlance towards personal media devices. Also, Apple probably holds a copyright on the term podcast.
Zencasts can be played on the Zen series of mp3 players, which include the Zen micro, Zen neeon, Zen V, and Zen Vision players. These players come with software (for the PC) called the "Zencast Organizer," which allows you to search and subscribe to a large amount of pod.. er, zencasts currently being produced.
Unfortunately, as many of the video casts that you can subscribe to are made for use with iPods, and thus are in mp4 format. Zen players do not have the built in ability to play files in this codec, though they come with video conversion software, aptly named the "Creative Labs Video Converter." This software is, unfortunately, very slow and prone to crashing your computer. I highly recommend that one converts the mp4's with different software and then transfer them to their Zen player. The uploading software for the players is actually very good, but you can also do it the oldschool way of dragging and dropping your media files into the folders on the player using Explorer, as Zen players automatically show up as external hard drives on your computer.
Zencasts produced with the intention for use on a Zen player usually use the wmv or wma codecs, as they are small files that Zen players have the built in ability to play. However, Zen players can also play files encoded in Divx, Xvid, and standard AVI and MPEG codecs.
So next time someone asks you if you got some latest podcast, and you own a Creative Labs mp3 player, you can snootily rub their apple-loving nose in it and say, "Sorry, I only listen to zencasts."