How many montiors do you have?

I have a single screen. You read that right. 1 screen. And it's not new. This is the part where, you ask "But it's a BIG screen, right?" Nope, not really. And I'm A-OK with it. So there. Not self conscious at all.

So that leads me to this question: what is the difference between a television screen and a computer monitor. I have friends who run an HDMI cable from their laptop to a TV, and it often looks a little weird. But I don't know why it would. What's the fundamental difference between these two types of screens?