What is the bouncing of light when it changes media

When light passes from one medium to another, part of it continues on
into the new medium, while the rest of it bounces away from the boundary,
back into the first medium.

The part of the light that continues on into the new medium is transmitted
light.  Its forward progress at any point in its journey is transmission. 

Its direction usually changes as it crosses the boundary.  The bending is
refraction.

The part of the light that bounces away from the boundary and heads back
into the first medium is reflected light.  The process of bouncing is reflection.