A complex number in which the imaginary part is not zero.
A complex number in the form a + bi where b is not zero: when a is zero, it is a pure imaginary number.
A type of complex number in which the multiple of i (the square root of −1) is not equal to zero. Examples of imaginary numbers include 4 i and 2 − 3 i , but not 3 + 0 i (which is just 3).
(complex analysis) A number of the form ai, where a is a real number and i the imaginary unit.