A jumper was a term for a child or young person who enjoyed jumping on objects, typically furniture, whenever the opportunity presented itself. Jumpers were often described as calm and quiet children when adults were present.
Ro Laren was a repressed jumper during her youth on Bajor amid the Cardassian Occupation. This was discovered during a conversation with Guinan in 2369 after both had been turned into children by a transporter accident. (TNG: "Rascals")