Damping
Damping controls unwanted tonearm movement during playback, helping to reduce repeated back-and-forth motion.
Here, damping means a mechanism that resists arm motion. Internal tube damping treats vibrations within the tube; a damped cueing lift slows lowering onto the record. These are different from damping the arm’s movement during playback.
Damping — Tonearm
Fluid trough usually means a paddle moving through silicone fluid, which resists motion; the catalogue also groups fluid-damped pivots here. Magnetic / eddy-current damping uses electric currents induced in moving metal within a magnetic field to oppose motion without mechanical contact. Both can control arm oscillation.
None means no motion damper, not an absence of all damping. Check whether a damper is fitted or only offered as an option, and whether it acts horizontally, vertically or both. Fluid damping does not necessarily cover both directions. Follow the arm maker’s fluid and adjustment instructions. The damping type alone does not establish better sound.