non-singular

In mathematics, a singular point of an algebraic variety V is a point P that is 'special' (so, singular), in the geometric sense that V is not locally flat there. In the case of an algebraic curve, a plane curve that has a double point, such as the cubic curvey2 = x2(x + 1) exhibits at (0, 0), cannot simply be parametrized near the origin. The reason for that algebraically is that both sides of the equation show powers higher than 1 of the variables x and y. In terms of differential calculus, if
See more at Wikipedia.org...