'Streaming' is where instead of purchasing a track to download, you simply listen to it over the internet. For the user this might be free, or they might pay a subscription so not to be interrupted by adverts. When you play a track on Spotify or iTunes without making a purchase, you are streaming.

For the musician, it doesn't pay too well. I've just looked at my sales report from Spotify who have recently paid me the princely sum of $0.00720538 for a streamed track. After CD Baby's cut and Paypal and currency conversion fees, the rest is to be split 5 ways between band members. We're not going to get rich! Of course, if you are a global star whose downloads are measured in millions then this starts to add up, for the rest of us ...