A foreskin is a piece of natural skin that is retractable and fits over the head of your penis (you can call it head, glans, or bell head). Some people may think it's bad (because some get it removed), but it's not bad at all and is natrual. It's just a natural part of the penis and adds extra pleasure during masturbation and sex (if you have one)
Some guys get this cut off at birth or when it's needed for religious reasons or medical reasons.
For more info, read this thread: http://www.virtualteen.org/forums/sh...ad.php?t=13121