Holodeck

Holodecks were a form of holographic technology used on Starfleet starships in a parallel universe. (COMIC: Assimilation²)

In an attempt to visit San Francisco, the Doctor's TARDIS accidentally took the Eleventh Doctor, Amy Pond and Rory Williams to the holodeck of the USS Enterprise (NCC-1701-D) in 2368. At the time, the holodeck was running the program Picard Dixon Hill Seven, set within a simulation of San Francisco. (COMIC: Assimilation²)

Other references
In the main universe, they were a fiction seen in the Star Trek franchise.

Izzy Sinclair, a longtime fan of the show, once claimed to have travelled with the Eighth Doctor despite his ship not having a holodeck because "beggars [couldn't be] choosers". (AUDIO: Izzy's Story) However, the Seventh Doctor had a room in the TARDIS where he showed Bernice Summerfield a 3-D holo-simulation of his first incarnation on Gallifrey. (COMIC: Flashback)

Andy Hansen compared an artificial bubble universe to the holodeck from Star Trek, but then realised Erimem did not known what Star Trek was. (PROSE: The Last Pharaoh)

Nardole compared the Shadow World to "the holodeck on Star Trek", shortly before he discovered he was part of the Shadow World himself. (TV: Extremis)

Jason Kane loved Star Trek and remembered the holodeck, but his clone, 2Jason, did not know about it. (PROSE: The Two Jasons)