Given a smooth map of differential manifolds, a point in the image manifold is termed a regular value for the smooth map if every point in its inverse image is a regular point, i.e. if the map from the tangent space at any point in the inverse image, is surjective.
Note that any point whose inverse image is empty, is by definition a regular value.
Definition with symbols
Let be a smooth map of differential manifolds. A point is termed a regular value of if for every , the induced map , is surjective.