0 (zero; BrE: , or AmE: , ) is both a number and the numerical digit used to represent that number in numerals. It fulfills a central role in mathematics as the additive identity of the integers, real numbers, and many other algebraic structures. As a digit, 0 is used as a placeholder in place value systems. In the English language, 0 may be called zero, nought or (US) naught , nil, or "o" . Informal or slang terms for zero include zilch and zip. Ought or aught have also been used historically. (See Names for the number 0 in English)

Signed zero is zero with an associated sign. In ordinary arithmetic, -0 = +0 = 0. However, in  computing, some number representations allow for the existence of two zeros, often denoted by -0 (negative zero) and +0 (positive zero). This occurs in the sign and magnitude and ones' complement signed number representations for integers, and in most floating point number representations. The number 0 is usually encoded as +0, but can be represented by either +0 or -0.