Coupling is a mechanical connection between two things.
The hose coupling is the metal piece on the end of a hose to connect it to extra hose or hose appliances. It is usually made of steel, brass, stainless steel or aluminum.
Rotating couplingA coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, though there do exist torque limiting couplings which can slip or disconnect when some torque limit is exceeded.