what is jailbreaking for ipod,?

i have an ipod touch everyone talk about jailbreaking it but i didn't understand what is it and if i jail break it what will i lose? can i install the new update ?? what are the benefits of jail breaking?,
first:
Read this hope i helps http://mac.blorge.com/2007/10/20/faq-iphone-ipod-touch-hacking-jailbre​aking/
second:
It's a way for people who didn't do their homework, and bought an iPod, and now regret it, to make their iPod more like other other media players, which, of course, they should have just gotten in the first place.