Docking arm

From Memory Alpha, the free Star Trek reference.

A docking arm was a large magnetic extension built into the launch bay of an NX class starship. The arm was used in docking procedures, such as a shuttlepod landing or departure. Officers aboard the vessel were able to remotely deploy the docking arm from the starship's bridge. (Star Trek: Enterprise)

The name was mentioned in ENT: "Fight or Flight" and "Hatchery".