To add to that, you have:
480p/480i
720p/720i
1080p/1080i
Technically 480p is high definition but with such large advancements in technology its kind of difficult to say its high definition at the present time, as when you say high definition one expects excellent video quality whereas 480p falls below the expected video excellence.
On top of that though, you actually need a TV that can display those resolutions. Then on top of that you need the best connection too to achieve best video quality.