I use the term in a lot of scenarios..usually a Jacker in my games use trickery or sabotage to get aboard and disable a ship at a critical point. Usually they have inside help picking targets and getting the travel routes,cargo manifests, an passenger lists, of a likely target ahead of time..such as a corrupt port official, or shady Broker.
this sort of criminal is a lot harder to deal with than a typical "Heave to , and prepare to be boarded" type.Those guys you can run from fight, or jump away from...if the Hijacker is already aboard...and you don't know it..then it's a different problem all together.
They send someone aboard as a passenger, or new hire/working passenger..that person disables the ships drives, or some other bit of sabotage to render a ship vulnerable.
If hes not detected he stays with the ship, and quits the next port "First trip with you guys and we get jumped..Heck no..You guys are jinxed, I'm out of here."
if he gets caught I usually include a blackmail bomb hidden in the guys luggage, or hidden aboard ship..."Touch me and I blow the ship." at which point the inside man tries to intimidate the crew into dumping cargo and waits for his buddies to pick him up.