What is video on demand?

I looked at BBC iPlayer first as an example of VOD.  On the website you are able to watch TV and radio programmes aired on the BBC in the last week.  You need internet to stream them but you are also able to download them if you don't have internet.  There is also a small amount of films and music videos normally from 'Live lounge ' sessions, BBC is known for doing.  iPlayer and other website like this are useful as you don't need to watch it on pirate websites that could damage your phone or laptop, and you don't have to download shows that take up a lot of storage.  Other examples of VOD are itv player, 40d and Demand 5.  These are good examples of convergence as on your phone you're able to watch tv shows, films, listen to radio shows and music.