A Podcast is either an internet audio or video show which you can download and then listen to at some future time.
Since I’m not in the Apple Universe, I use Gpodder.org as a way to subscribe and download shows to my computer. I then move them to one of my devices and listen to the show at my convenience – usually when I’m gardening. Below are the shows I am now listening to – Car Talk is my favorite. My favorite device for this is a Sansa Clip which also has a slot for a SDHC card.
Here’s the NPR podcast list.