Hacking is a lot of things to alot of people, there is no good way to explain it. However, it is certainly not limited to computer nerds breaking into computer systems. Hacking might be finding a better way to make a program work...or it might be playing games, it might be political with an anarchist agenda, it might be a process or product, thing or theology, a way of life or just something you do once...it might be solving a riddle, getting even, causing panic, creating knowledge. Hackers are men, women, children, and if their email address are correct lobsters from Mars. And hacking is certainly not limited to computers...are hip hop artists musical hackers? Was McLuhan a social hacker?
What is a Hacker I suggest you do some reading at EFF's Hacker Archive