More specifically the term refers to officers involved in sting opereations. (Narcotics, Prostitution, Organized Crime etc.)
The 'Jump Out Boys' are usually either the swat team, or the cops on stake outs inside the sound van, listening in on wire taps or wired informants. When tipped off, or alerted, these officers are known to jump out of the vehicle and subdue suspects by force, thus the term 'Jump Out Boys'.
They ride in unmarked vehicles, typically vans, trucks, and vehicles without windows.
Some gangs and/or squads are known tocall themselves 'Jump Out Boys' due to their simmilar, jump out style.
"I got hemmed up by the 'jump out boys' last night. I was walkin home from the spot and they came out of nowhere!"