A hologram is an artifical contruct, generated by an emitter.
Holograms were designed to perform specific functions, specifically involving interacting with pony customers. They could fill in the role of receptionists and salesponies when needed, though they are only programmed with a limited number of functions.
The Apple Bot can generate it's own holographic field, giving it the appearance of a filly aged Applebloom. A holographic receptionist was encountered by Blackjack inside Flash Industries headquarters. It turned hostile when it noticed Blackjack's PipBuck was carrying EC-1101.
The Casino Royale and the resort town around it, has holographic emitters. Two of these emitters generated two salespony holograms of Flim and Flam, the holograms caused the Build-Me-Up Buttercup robot toys to attack Dead-Shot. Inside the Casino Royale, holograms had been placed throughout the high class hotel, these holograms could fire off beams of magical energy, though they shut down once their emitters had been damaged. The Casino Royale holograms could reboot, thanks to the nanobot technology built into the hotel, that would rebuild the destroyed emitters.
Murky Number SevenEdit
Murky encountered a holographic version of Pinkie Pie, a recording that was made with a message for him. The hologram behaved and acted much like Pinkie Pie, even breaking the normal rules of reality by touching Murky, despite that being impossible. The hologram engaged Murky in a song and dance routine, also summoning several Sprite-bots acting as supporting singers.
Holograms are based on the same constructs from Fallout 3's expansions Point Lookout and Mothership Zeta. The Casino Royale's holograms are based far more on the holograms from Fallout: New Vegas's expansion, Dead Money. See Holograms on the Fallout wiki for more information.