:) I will answer ONLY the railway part! In general terms, it means something else!
Coupling in Railway terms is attaching one/two/three bogies together either by using a CBC coupler which automatically fits into the other bogies coupler or by a hook and screw type arrangement. Coupling of the engine to the rake is also done in similar fashion. The CBC type requires only the engine to nudge the bogies together and the couplers fit into each other.. ditto for attaching the engine. In the hook and screw type arrangement, the oblong 'square' piece of metal fabricated is lifted up manually, and inserted into the hook of the adjoining bogie. Then the screw type mechanism is tightened manually again to make the...
more... screw and hook to be firmly in place, preventing loose connection, by tigtening the screws to the maximum level possible. The difference in screw type coupling for engines, is that the ALP/LP also inserts over the hook coupled, another hanging square shaped metal piece to prevent the screw type coupler from jumping out during fast running. If that piece falls out, there is a loud sound which alerts the LP/ALP that something has/is going wrong on the run, and they try and immediately check whether there is any fault with the coupling of the rake, and take appropriate action.
The second part of this coupling process is to attach the air/vacuum carrying tubes of sufficient tensile strength together between the engine-bogies-Last vehicle. When this is attached, the driver releases the brake pressure, and then starts building up the pressure to the required PSI in the air brake hose, which is also reflected in the Guard's cabin. In turn to check that it is working properly, the guard, when assuming duty, which is after the LP/ALP have taken charge, again releases the brake pressure built up, and then the LP/ALP again builds up the pressure throughout the whole train, and when both readings (in the loco and the guard's van) are the same, the guard releases the train's readiness for departure.
I will be happy if someone can elaborate further on this ! Good wishes.