A non-integer is a number that is not a whole number, a negative whole number or zero. It is any number not included in the integer set, which is expressed as { ... -3, -2, -1, 0, 1, 2, 3, ... }.

Examples of non-integers include decimals, fractions and imaginary numbers. For example, the number 3.14, which is the value for pi, is a non-integer. Another non-integer is the mathematical constant e, known as Euler's constant, which is equal to about 2.71. The Golden Ratio, another non-integer mathematical constant, is equal to 1.61. In fraction form, 1/4, equal to 0.25, is also a non-integer.