Those who use the Hindu-Arabic numeration system are all familiar with the concept of “zero” (0) and its importance. The symbol “zero” represents a valuable placeholder; it is also the additive identity element of an algebraic system (when a number and its additive inverse add up to 0); and finally, it is the starting point in measurements. The zero symbol is also called a cipher (no relation to sending secret messages) or the symbol for the absence of quantity, although be aware that cipher can also mean any Hindu-Arabic numeral. (Interestingly enough, the name “zero” is derived from the Arabic sifr, which means “cipher.”) In other words, zero is naught (nothing, or from the Old English, nāwiht, meaning “not” [na] and “thing” [wiht]).

Mathematicians also use the word non-zero to represent a quantity that does not equal zero. A real non-zero number must either be positive or negative; a complex non-zero number can be the real or imaginary part of the equation. (For more information about complex numbers, see above.)