Imaginary number

In mathematics, an imaginary number is a complex number that is not real. The term is not generally used because complex numbers (e.g., $3+4i$), have two components, a real part (in this case 3), and an imaginary part (in this case 4). A complex number is said to be real if the imaginary part is 0, and in all other cases it is non-real. In most cases, when people speak of imaginary numbers, they are not referring to complex numbers which are not real, but complex numbers with a real part of 0. For clarity, such numbers are usually called pure imaginary.

For more information, see the article Complex number.