FOCAL POINT

In optics, the Airy disk (or Airy pattern) are descriptions of the best focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light.

The diffraction pattern resulting from a uniformly-illuminated circular aperture has a bright region in the center, known as the Airy disk which together with the series of concentric bright rings around is called the Airy pattern.

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge.
Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle.