what does it mean if "b^2 - 4ac < 0" for a quadratic equation (eg y = a*x^2 + b*x + c)

The question comes from the quadratic equation r = (-b +- sqrt(b² - 4ac)/2a where r is the root or x coordinate where the line crosses the x-axsis (the y coordinate is always 0). If b² - 4ac < 0 then to find the root you whoud have to take the sqrt of a negative number which doesnt exsist (at least it doesn't for standard maths alevel students) and so the line doesnt have any roots. This means that it doesnt cross the x-axsis.