Zero: As a mathematical idea, the absolute zero obtained by the subtraction of equal quantities (expressed by a - a). In physical measurement, a lower limit or point of origin, as in the zero of a scale or the absolute zero of temperature.

As a symbol, the absence of all number or quantity, necessary in our system of notation in order to preserve the principle of positional value by occupying positions which would otherwise be filled by one of the nine digits.

Its symbol, the circle, represents at once nothing and everything; it is the symbol of boundless infinity; and a circle may be defined either as a single undivided and unterminated line, or as an infinite number of infinitely short lines.