A jalp is a pushy bum who hassles you for money or squares. The jalp usually uses three methods, outright demanding money, using a bunk story about some absurd misfortune to cover up the fact that they're going to use the money for booze/crack, or trying to sell you some stolen goods/drugs/secondhand porn for money.
"Hey man, I was just on the northside and ten mothas jumped me and hit me with a pipe and then my mom died and then my car broke down, can I have twenty dollars? I'll pay you back next week when I get my inheritance."
"Get out of here, you jalp!"
"Wanna buy an Ipod? Twenty dollas"