Mechanical seal

A mechanical seal is a piece of hardware that is used in places where two other pieces of hardware are connected. The idea of the seal is to prevent or limit leakage. Depending on the use case, there are different designs of these seals. Very often, the substance used for sealing is also important.

Seal on a lock.

When water is still dripping from a tap that is closed, this means that the mechanical seal (that should prevent this) is broken.