Hologram

A hologram is an artificially created image using photons arrainged in a manner to better display information...or trick people, depending on the situation at hand.

Generation 1 cartoon
The Autobot Hound often made use of holograms. While on guarding Ravage with Mirage, Hound came up with the idea to use a hologram to trick the Decepticons and lead them into an ambush. Optimus Prime agreed, and Ravage was allowed to escape, believing he had learned of a military base with large amounts of rocket fuel. Megatron, however, saw through Ravage's escape, sending the Decepticons to the real base, while he went with a group of shoddy constructions to rub it in Prime's face. The hologram worked, though...

IDW comics continuity
Recongnizing that the Autobots lack of drivers would attract attention, they used Holomatter avatars to avoid detection.

Beast Wars/Beast Machines
By the Beast Era, holograms were in more wide scale use, including such things as entertainment and military use. The Axalon and the Darksyde both made extensive use of hologram technology to run simulations and observe events in real time. On Cybertron, there were holo-chips which allowed Transformers to interface with them and see things virtually&mdash;some of which were not always virtous, if you get our meaning. .

Movie
After introducing the Autobots, Optimus Prime showed Sam Witwicky and Mikaela Banes a hologram of the devastation Cybertron suffered during the war with Megatron. The Decepticons also made use of holograms, using a single, mustached male as a display to avoid attracting attention.