An Ideal point is a point in infinity,it has a 0 in the z coordinate and we can not divide by 0, the problem we have therefore is that the ray that defines it, is parallel to the image plane, and doesn’t intersect with it.
On the other hand, the ideal line is a line that it’s normal is parallel to the image plane.
That means that the plane that it defines is also perpendicular to the image plane, and has a 0 coordinate on the z coordinate.
That means that it’s formed by the rays that go through the origin or principle point, which is in most cases, the center of the image.
