Subscript, is character that placed at a lower height than some other characters. These elements are widely used in chemistry, to express the formulas of some substances, such as Oxygen O.
A superscript is a character that is raised higher than other character. This is something that can be very useful, such as expressing the surface of a building in square meters (m²). It is also very commonly used in mathematics and chemistry, to express the oxidation state of a certain element such as x².