HD meaning in General ?

The Holodeck is a fictional device from the television franchise Star Trek which uses "holograms" (projected light and electromagnetic energy which create the illusion of solid objects) to create a realistic 3D simulation of a real or imaginary setting, in which participants can freely interact with the environment as well as objects and characters, and sometimes a predefined narrative.

In several series, holodecks are an amenity available to the crew of starships. In the series Star Trek: Deep Space Nine, a similar device is referred to as a holosuite, operated by the owner of the space station's bar, Quark, who rents them out to customers.

From a storytelling point of view, the holodeck permits the introduction of a wide variety of locations and characters, such as events and persons in the Earth's past, or imaginary places or beings, that would otherwise require the use of plot mechanisms such as time-travel or dream sequences. Writers often use it as a way to pose philosophical questions.