If you've ever looked through a View-Master, you've seen a hologram — an image or photograph that appears to be three-dimensional.
Holograms sometimes appear on credit cards, passports, and driver's licenses as security against forgery, and they are also occasionally used in art. The process of creating a hologram is complicated and scientific, usually involving a special kind of laser. The word hologram was invented by Dennis Gabor, the scientist who developed holography in 1949, by combining the Greek holos, "whole," and gramme, "line."