"Streaming" refers to the downloading of a video, TV, movie, music, radio, etc. over the Internet, rather than watching/listening to it on a satellite TV service (e.g. Dish Network, DirecTV), on a blu-ray player, DVD player, VCR, CD player, radio, etc.

You can stream on most Internet-connected devices such as a Smart TV, a TV with a streaming device attached (e.g. a Roku, AppleTV, Firestick, etc.), a smart phone, a computer/laptop/tablet).

HowStuffWorks has a comprehensive guide on streaming.