A forced plasma beam was a type of beam fired from some hand-held plasma weapons, such as the hand-phasers used by the Ferengi and weapon implants used by Borg drones. The plasma beam was traceable to its origin with a tricorder.
In 2369, the entire staff of 274 Starfleet personnel on the Ohniaka III Research Station were killed with forced plasma beams used by the Borg. (TNG: "Descent")