Optics (or Ray Optics) : The branch of optics is treated
by the method of light rays. Under ordinary situations,
travels i straight lines. This reasonable assumption has
led to a ray model. The ray model is found very successful
in explaining phenomena like refraction and formation of
images by mirror and lenses. Since these explanation involve
straight line ray at various angle, it is called geometrical
optics (or ray optics).
In other words,
The branch of optics which is treated by the method of light
rays is called ray optic or geometrical optics.