在数学中，被除数的除数（分母）是零将某数除以零，可表达为，是被除数。在算式中没有意义，因为没有数目，以零相乘（假设），由于任何数字乘以零均等于零，因此除以零是一个没有定义的值。此式是否成立端视其在如何的数学设置下计算。一般实数算术中，此式为无意义。在进程设计中，当遇上正整数除以零进程会中止，正如浮点数会出现NaN值的情况，而在Microsoft Excel及Openoffice或Libreoffice的Calc中，除以零会直接显示#DIV/0! 。

In mathematics, division by zero is division where the divisor (denominator) is zero. Such a division can be formally expressed as a/0 where a is the dividend (numerator). In ordinary arithmetic, the expression has no meaning, as there is no number which, multiplied by 0, gives a (assuming a≠0), and so division by zero is undefined. Since any number multiplied by zero is zero, the expression 0/0 also has no defined value; when it is the form of a limit, it is an indeterminate form. Historically, one of the earliest recorded references to the mathematical impossibility of assigning a value to a/0 is contained in George Berkeley's criticism of infinitesimal calculus in The Analyst ("ghosts of departed quantities").