Why do we call imaginary numbers "imaginary numbers"? As far as I can tell, there's nothing really imaginary about them. They exist. They're used all the time. What makes them so "imaginary"?
Those numbers were once poorly understood and regarded by some as fictitious.The use of imaginary numbers was not widely accepted by many .It was left to Euler and others to use them. Euler, in his wrote in his Introduction to Algebra
In short, it is a matter of acceptance of or the lack of it which gave them the name.