1 (often with at, on or with) to give a light knock (on or with something) -- leicht klopfen
He tapped at/on the window.
2 any of several types of device (usually with a handle and valve that can be shut or opened) for controlling the flow of liquid or gas from a pipe, barrel etc ; faucet( American) -- der (Wasser-, Gas-, Öl-)Hahn
Turn the tap off/on!
4 to attach a device to (someone’s telephone wires) in order to be able to listen to his telephone conversations -- abhören
My phone was being tapped.