Holography is the art of 'lensless photography'. It is typically formed by reflected light captured on film. For example, a laser would hit an object. The object then reflects the light, and the reflection of the light is what is captured on the film. The images from a hologram contains more information than a traditionally photograph. The image is three dimensional and exhibits parallax.
Holograms have cool properties that aren't displayed in photos. My personal favorite is that in a transmission hologram, the one previously explained, every piece of the film contains the whole image. So If you cut of a tiny corner of the film, you see the same image as the complete hologram. So you can cut the film up into a hundred different pieces and the image would be the same on all of them.
Also, holographic images scale with wavelength. This is exciting because in theory, one could make a holographic image using x-rays, and view it using visible light. Although this has yet to be done, the potential is there and the benefits can be significant.
Holograms are often thought as movie props, or just a smoke and mirror science, but holography is a very important part of the optics field. Holography has the potential to do many things. Holography is used in the laser lab in downtown Rochester. Holography can be used you decrease the size of lasers, which will help in power alternatives in the future. Holograms, while very fun, are also very useful.