Not an expert. Also, far away. For me, TRIM is a verb. It implies through common usage the implementation of a small aerodynamic device to position a control surface in the airstream such that no continued force is necessary to keep it in place. It relieves the operator of a consistent and irritating need for pressure to be applied to the controls. As such it implies an adjustment in control pressure so that an attitude may be extended for a length of time. As used in large and flyable Horizontal surfaces, it takes on a somewhat different meaning. Rather than freezing a small device in place to relieve the pressure needed to maintain an attitude, THS essentially moves the whole kit and changes the "Angle of Incidence" of the Wings themselves.
So a THS is not strictly speaking a transitory attempt to relieve Pressure on the Controls, it changes the aspect of the airframe itself. It is in essence the 'Elevator'. It makes 'permanent' a flight attitude commanded by the FCS. It 'follows' elevator input, giving them a great deal more authority in Pitch.
So see, I am not an expert, as my clumsy explanation proves.