Welcome to the land of complex numbers, aka argand plane.
and yes,
it's originated by the equation,
the fundamental theorem States a polynomial equation has the same number of roots as its degree. though that equation, doesn't in real plane, it has roots ±.
There is no square root of -1. Although 1 can be derived from 1x1, 1 is not the square root of 1 as positive 1 x positive 1 will always give a positive 1. Similarly, negative 1 x negative 1 will always give a positive 1 hence it is not possible for -1 to have a square root.