What is jailreakin in dummy terms?

[nicnac90]

hell tere im quite thick and would like to know what jail breaking is and is it really worth doin can you please xplain though in realy realy simple terms

[psylichon]

I think one of our moderators put it best:

http://www.everythingicafe.com/forum/iphone-modifications/what-jailbreaking-is-and-how-to-do-it-27443.html