complex number

noun

1. a mathematical expression (a + bi) in which a and b are real numbers and i2 = −1.

noun

1. any number of the form a + i b, where a and b are real numbers and i = √–1See number (def. 1)

1. A number that can be expressed in terms of i (the square root of -1). Mathematically, such a number can be written a + bi, where a and b are real numbers. An example is 4 + 5i.