This document defines liquid crystals as an intermediate state of matter between solids and liquids. It provides a brief history of liquid crystals, noting their discovery in 1888. It describes the four main types of liquid crystals - smectic, nematic, cholesteric, and columnar - and how they differ in molecular arrangement and mobility. Examples of thermotropic and lyotropic liquid crystals are given. The document outlines some key properties of liquid crystals and lists some pharmaceutical, food, and dermal applications that exploit these properties. Characterization techniques for liquid crystals are also summarized.