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. Names for the number 0 in English include zero, nought or (US) naught , nil, or — in contexts where at least one adjacent digit distinguishes it from the letter "O" — oh or o . Informal or slang terms for zero include zilch and zip. Ought and aught , as well as cipher, have also been used historically.