Sounds like you're talking about a movable horizontal stabilizer. It's aft structure is attached to the vertical stabilizer or aft fuselage structure by hinge fittings attached to each structure and connected to each other by hinge pins. The forward end of the horizontal is attached to a jackscrew(s) which extends upward from the pitch trim actuator driven by hydrualic and/or electrical redundant motors. When the pitch trim switch is operated by the pilot or the autopilot schedules pitch trim, the motor activates and turns the jackscrew in the direction that will raise or lower the leading edge of the horizontal stabilizer, changing the amount of tail downforce being produced. The elevators are hinged to the trailing edge of the stabilizer and are operated by the pilot or autopilot to control aircraft pitch attitude. The pitch trim is operated to relieve the need to hold the elevators deflected to maintain desired pitch attitude. The failure of the jackscrew assembly led to the loss of control of AL 261 a few years ago off the California coast. An improperly assembled jackscrew attachment caused a similar loss of an IAI 1124 Westwind in Pennsylvania also. A jammed stabilizer is a serious problem since full elevator travel cannot overcome the effect of the stabilizer when it is near full travel.
Best,
Westhawk