A very nasty fungus that grows on the bottoms of feet, usually after consuming too much of an alcoholic beverage. It is green, moldy, and continues to reproduce itself in the swells and fat cells of your feet. The cure for Ja Rule is to go to your local doctor and get the pill "Tupac" perscribed to you.
"Friend 1: Yo man, i was clubbin' last night with my friend Fat Joe, and then Shaq came and stole his cheeseburger. Fat joe cried, so i took him home, then when i woke up, I had ja rule on my feet!"
"Friend 2: I've had ja rule before, you need to take a dose of tupac"