A superscript is a number, figure, symbol, or indicator that is smaller than the normal line of type and is set slightly above the baseline.
A subscript or superscript is a number, figure, symbol, or indicator that appears smaller than the normal line of type and is set slightly below or above it – subscripts appear at or below the baseline, while superscripts are above.
Subscripts and superscripts are perhaps best known for their use in formulas, mathematical expressions, and descriptions of chemical compounds or isotopes, but have many other uses as well.
In professional typography, subscript and superscript characters are not simply ordinary characters reduced in size; to keep them visually similar to the rest of the font, typeface designers make them slightly heavier than a reduced-size character would be. Likewise, the amount that sub- or superscripted text is moved from the original baseline varies by typeface and by use.
n typesetting, such types are traditionally called superior and inferior letters, figures, etc., or just superiors and inferiors. In English, most non-technical use of superiors is archaic.
Superior and inferior figures on the baseline are used for fractions and most other purposes, while lowered inferior figures are needed for chemical and mathematical subscripts.
Source:http://en.wikipedia.org/wiki/Subscript_and_superscript
