Full HD camcorders are capable of showing high definition images that are up to five times as sharp and detailed as old style 'standard definition' images. When you see a camcorder which is '1080p' (like the Panasonic SD90) it is able to record in full HD and offers the highest possible levels of detail for your recordings.
So what can you do with the footage in HD? You can play back 1080p video on your computer, or your HD television. You might also want to create your own blu-ray discs (as long as you have a blu-ray player to watch them on). If you're in the market for a camcorder, make sure it is 1080p. There's some good info on all things 1080p over at Wikipedia. And there's a very helpful section at About.com on HD camcorders.
