The angle made by the incident ray with the normal at the point of incidence is known as the angle of incidence.

The angle made by the refracted ray with the normal at the point of refraction is known as the angle of refraction.

Light changes its direction when going (obliquely) from one transparent medium to another transparent medium. This is called the refraction of light.

Absolute Refractive Index of a medium is defined as, the ratio of the magnitude of the velocity of light in vacuum, to the magnitude of the velocity of light in that medium.

The process of separation of light into its component colours, while passing through a medium, is called the dispersion of light.

When light enters a rarer medium from a denser medium, it gets partially reflected i.e. part of the light gets reflected and comes back into the denser medium as per laws of reflection. This is called partial reflection.

When light travels from a denser medium to rarer medium, if the angle of incidence is greater than the critical angle, there is no refraction of light and all the light is reflected in the denser medium. This is called total internal reflection of light.

When light travels from a denser medium to rarer medium, the angle of incidence for which the angle of refraction becomes 90°, is called the critical angle.