Podcasts aren't streaming. And they can be either audio or video.
Podcasts typically have "episodes" released at intervals. Using iTunes, you can subscribe to a podcast. iTunes will automatically download each new episode and load it on to your iPod when you dock it. There are other ways to get podcasts, but this is the easiest.
For example, CNET has a daily tech news audio podcast. Every night, I dock my iPod to charge it and download the podcast. Suicide Girls releases a new video every week via podcast. I even get weekly italian lessons via podcast.
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