The term "tetragonal" refers to a specific type of crystal system in which the unit cell has two equal axes and one axis that is different in length. This results in a rectangular base with a height that differs from the base dimensions. Tetragonal crystals are one of the seven crystal systems in crystallography, which is the study of crystal structures and their properties. Common examples of tetragonal crystals include zircon and rutile. These crystals can exhibit unique optical and physical properties due to their symmetrical arrangement. Understanding the tetragonal system is essential in fields like materials science and mineralogy, where the arrangement of atoms influences the behavior of substances.