Arch

An arch is a holographic structure containing virtual computer control panels and interfaces; they are a feature of Starfleet holodecks of the 24th century. When a program is running in the holodeck, the arch could be made to materialize by voice command when participants wish to modify the current program, communicate throughout the ship, or access most general computer functions. The arch is visible to participants, and even though the holographic characters generally do not perceive the arch, there have been exceptions. 

A related voice command, "Exit", is used to remove the holographic environment around the holodeck door when participants wished to leave the holodeck without closing the program. (Star Trek: The Next Generation, et al.)