What is a complex number?
A complex number is any number that can be represented as the sum of some number on the real number line and some number on the imaginary number line, a number line perpendicular to the real number line that contains multiples of sqrt(-1), which is more commonly denoted as i.
Complex numbers find applications in AC electronics in calculating impedance. They are also used in producing fractal images, and they turn up in quantum mechanics as well.
The real numbers are a subset of the complex numbers (specifically, they're complex numbers where the imaginary part happens to be zero).
The question refers to the "following". In such circumstances would it be too much to expect that you make sure that there is something that is following?