Podcast

A podcast is a ‘multimedia digital file made available on the Internet for downloading to a portable media player, computer, etc.’  Err?  OK.  I think I understood that.  But isn’t a blog or an ordinary webpage often multi-media?  And isn’t a blog/webpage also available on the Internet?  And can’t it also be downloaded to a portable media player like a phone or a computer?  I tried to understand the difference by reading the article by the Goddess Wiki but it included phrases like ‘It is very much a horizontal media form’ – so I gave up.  Can anyone give me a clear and easily understood explanation of what a podcast is?