In chemistry and physics, the term glass itself is a mutable concept: It includes the substance we know as window glass, but it may also refer to a range of other materials with properties that can be explained by reference to glass-like behavior, including, for instance, metals, plastics, proteins, and even biological cells.
While it may give the impression, glass is anything but conventionally solid. Typically, when a material transitions from a liquid to a solid state the molecules line up to form a crystal pattern. In glass, this does not happen. Instead, the molecules are effectively frozen in place before crystallization happens. This strange and disordered state is characteristic of glasses across different systems and scientists are still trying to understand how exactly this metastable state forms.