A liquid crystal is exactly what it sounds like: part liquid, part crystal, all awesome. From a distance a liquid crystal seems to be fluid in its behavior and organization, but take a closer look and you realize that it has some organized structure reminiscent of a solid crystal. The first mention of liquid crystals comes from an experiment in 1888 by Friedrich Reinitzer. The results of his experiment seemed to show that cholesteryl benzoate had two melting points, one that formed a cloudy liquid and one that formed a clear liquid. Upon closer analysis by a physicist it turned out that the intermediate phase has composed of crystallites.
An interesting phenomenon and also the greatest application of liquid crystals is their ability to change between a set of phases under certain conditions, such as temperature, electrical charge or composition. This has been exploited both artificially and naturally, where certain membranes and proteins behave as liquid crystals. Specifically this is useful because the internal order of the crystals can let certain polarizations of light through while blocking others. This is the basic principle behind Liquid Crystal Display, or LCD, televisions. The image above shows two phases, the less organized nematic phase is seen on the left while the smectic phase is shown on the right letting only certain light polarizations through.