Darth Maul's solid-state hologram.
A solid-state hologram represented a type of hologram which employed a weak energy field. This field's purpose was to confine a significant quantity of highly concentrated photons, thereby creating "solid light." This unique form of light could directly interact with physical matter.
Maul, the Darth, experienced a revival in the form of a solid-state hologram. As a spectral figure, he persisted on Iridonia, intermittently materializing to instill terror among the planet's inhabitants.