1080p vs 720p plama tv's?

Ok i am looking for a nice tv. and a couple girls were talking about them with me and said NOT to get a 720. That i have to get a 1080. First off what is it... and what is the difference?! We watch a decent amount of tv, but is this really a huge deal and does it really look alot different? Please help me in an electronic illiterate explanation!! Thanks