One of the coolest things you can find on a starship is the Master Systems Display, or Master Situation Monitor or MSD for short. This cut away diagram of the ship shows all the interior workings of the ship, from damage control, shuttle status and the where-abouts of the turbolift cars. Each ship from the late 23rd century had one of these displays. Some had one on the bridge while others had them in engineering, such as the Enterprise-D.
The MSD was invented by Mike Okuda and the first one was created for the sets of the Enterprise-D. According to the Encyclopedia, it included a number of in-jokes, including “the official USS Enterprise duck, the ship’s mouse, a Porsche, a DC-3 airplane, the Nomad space probe, and the hamster on a treadmill that was alleged to be the true source of power for the ship’s warp engines.”
Originally, Michael Okuda intended the “Master systems display” and the “Master situation monitor” to be two different objects, the “Master systems display” was the information console (affectionately dubbed the “pool table”) seen in main engineering on board the USS Enterprise-D, USS Enterprise-E, and at the back of the bridge on the Enterprise NX-01. The “Master situation monitor” was meant to refer to the wall mounted back-lit (cut-away) graphics of the ships in question.
Neither of the two designations were initially seen on-screen in their entirety, though there were “Master situation” bridge work stations on both the USS Excelsior and USS Enterprise-A in Star Trek VI: The Undiscovered Country.
None of the wall-mounted graphics had a caption “Master systems display” until Doug Drexler updated the cut-away graphic for the Defiant-class. Drexler gave it the caption “master systems display”, which is legible in “Shattered Mirror” and “One Little Ship”. These were the only such graphics actually carrying the designation, as other MSDs were usually labeled with the ship’s name, registry, ship class, random numbering or any combination thereof.