0 (zero; BrE: /ˈzɪərəʊ/ or AmE: /ˈziːroʊ/) 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 (/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. Ought and aught (/ˈɔːt/), as well as cipher, have also been used historically. An integer is a whole number that can be either greater than 0, called positive, or less than 0, called negative. Zero is neither positive nor negative. Two integers that are the same distance from the origin in opposite directions are called opposites.