Zero, written 0, is both a number[1] and the numerical digit used to represent that number in numerals. It plays 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 (both pronounced /ˈnɔːt/), nil, or "o". Informal or slang terms for zero include zilch and zip.[2] Ought or aught (both pronounced /ˈɔːt/), have also been used.[3]