A faucet or tap: the device that controls the flow of water from a pipe, typically turned to let water out.
蛇口をひねったらお湯が出た。
When I turned the faucet, hot water came out.
台所の蛇口から水が漏れているので修理してもらった。
The kitchen faucet was leaking, so I had it repaired.
蛇口を閉め忘れて床がぬれてしまった。
I forgot to turn off the tap and the floor got wet.