Holography is the science of producing holograms, an advanced form of photography that allows an image to be recorded in three dimensions. The technique of holography can also be used to optically store and retrieve information.
The Ancients had technology to make a solid holographic guardian and holographic sword, as well as a fully interactive teaching program and most probably other similar programs. The Asgard also developed a holographic pedestal to allow them to communicate with others by projecting holograms onto nearby ships or broadcasting them to other projectors light-years away. Other minor races also developed hologram technology over time. (SG1: "Thor's Chariot", "Red Sky", "Revelations", "Avalon, Part 1", "Camelot")
Ancient holograms are the most advanced; in addition to the ability to transmit lifelike holograms over great distances, including sound, they were also capable of simulating substance, creating a hologram which can fully interact with its environment. (SG1: "Avalon, Part 1")
Ancient ships also possess holographic heads up displays and can project holograms with sound onto other ships even when traveling at 99.9% light speed, although (at least on Aurora-class battleships) this speed hinders their ability to receive sound from the hologram. (SGA: "The Return, Part 1")
Atlantis has a whole room which contains a large hologram emitter to display holographic information from the Atlantis database, and in an alternate timeline the whole city was capable of projecting holograms anywhere within it. It is unknown if this feature was always present since the Ancients constructed the city or if it was an upgrade performed by the Tau'ri after they discovered it. (SGA: "The Last Man")
Ancient hologram technology was also frequently combined with their impressive Artificial Intelligence software to create lifelike interactive holograms, including the one used in the teaching program on Atlantis. In an alternate reality, the Tau'ri were able to program Dr. Rodney McKay's knowledge and personality into a hologram to be run on Atlantis' projection systems, but it is unknown if the software behind it was Ancient or not. Due to the amount of knowledge the hologram possessed, it is possible that some form of neural interface was used to copy McKay's mind; the Ancients have been proven to possess such technology, as have the Asgard (though the side effects of the Asgard technology have not been seen). The Tau'ri would have had access to both technologies. (SGA: "The Last Man")
The Asgard can create holograms that can project themselves, with sound, over long distances (for example, to a planet's surface from a ship). Two projectors working in tandem can be used as a three-dimensional subspace communication relay. They can also create holograms through an active Stargate. This technology is later given to the Tau'ri, as well as stolen by the Goa'uld. (SG1: "Thor's Hammer", "Thor's Chariot", "Nemesis", "Revelations")
The Goa'uld also use hologram technology for various purposes. They are most frequently used in heads up displays on their Tel'taks and the Pel'taks of Ha'taks. Besides these uses there exist smaller devices to create holograms for different purposes, like the Vo'cume projector, which can display a large hologram of a person. The Tok'ra also possess a small device capable of displaying holograms. After Anubis stole knowledge from Thor using a mind probe, he and Ba'al began to incorporate Asgard holographic technology onto their ships. (SG1: "Rules of Engagement", "Seth", "Revelations")