"Parcel media" refers to playing music, movies, webpages, & more on your land parcel(s) in Second Life. Once you learn how, it's easy to do.
We have a helpful selection of articles in our Knowledge Base detailing how you can play parcel media. In particular, see:
You can also watch video tutorials.
What will play?
Any format that QuickTime supports should work inworld, as well as standard webpages. So a good general rule is to try to play URLs in QuickTime Player or your web browser.