A complex number is a number of the form where a and b are real numbers and i is the imaginary unit. To put it mathematically, i is the square root of negative 1.
Some people like to think of it as .
Either way, it is the same thing. It is called an imaginary number because it is not part of the real numbers. It isn t greater than or less than anything. Try as you might, there is nowhere to put i . This is because i is outside the number line.