There is no word 'JEB', at least in standard English. It might be an acronym for 'Java Enabled Browser' or 'Journal of Experimental Biology'. Alternatively, it could be an abbreviation of the biblical name, 'Jebediah'. The town of Springfield in The Simpsons was founded by Jebediah Springfield!
Finally, in urban slang, it is apparently used to mean the end of the penis! Is that the usage you're after? If so, I have no idea of its origin.
On second thoughts, it's possibly a corruption of the word 'jib'. One meaning of this is the boom of a crane and a 'jib-boom' on old sailing ships was an extension of the bowsprit, a spar that sticks out at the front of old sailing vessels. This double suggestion of "something that protrudes at the front" may well be the connection!