Joy can also be used as an expression of success, and can be used (with its partner, No Joy when giving instructions).

Example: "Place Tab A into Slot B. If Joy, then place Tab B into Slot C. If No Joy, widen Slot B and repeat."

Example 2: "Hey, the date last night, joy/no joy?" "Joy. I'll tell you more later"

This probably originated as a military slang, and that is probably where "Joy" is applied most frequently. In military terms, Joy can mean anything from "successful aquisition of a target" to "target destroyed" or "enemies captured".