Definition of

Complex Number

Complex Number

A combination of a real and an imaginary number in the form a + bi

a and b are real numbers, and
i is the "unit imaginary number" √(−1)

The values a and b can be zero.

These are all complex numbers:
1 + i
2 − 6i
−5.2i (an imaginary number is a complex number with a=0)
4 (a real number is a complex number with b=0)