noun
stopcock; stop valve; shut-off valve
A valve used to stop the flow of water, typically in plumbing or water supply systems. Often refers to the main shut-off valve for a building or fixture.
水道の修理の前に、止水栓を閉めてください。
Please close the stopcock before repairing the water pipe.
この建物の止水栓は地下にあります。
The shut-off valve for this building is in the basement.
蛇口 is a faucet or tap at the point of use, whereas 止水栓 is a shut-off valve often located upstream or in a service line.
Compound of 止水 (shisui, 'stopping water') + 栓 (sen, 'plug, stopper, valve').