0 (zero; /ˈzɪəroʊ/) is both a number[1]and the numerical digit used to represent that number in numerals. The number 0 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 (UK), naught (US) (/ˈnɔːt/), nil, or—in contexts where at least one adjacent digit distinguishes it from the letter "O"—oh or o (/ˈoʊ/). Informal or slang terms for zero include zilch and zip.[2] Ought and aught (/ˈɔːt/),[3] as well as cipher,[4] have also been used historically.[5]