b² - 4ac is the discriminant of the quadratic equation
it will determine whether or not the roots are real or imaginary
when:
b² - 4ac > 0, roots are real and unequal
b² - 4ac < 0, roots are complex
b² - 4ac = 0, roots are real and equal
b² - 4ac < 0 and b=0, roots are purely imaginary
