Interface
The question is too vague for a definitive answer; depending on context, "surface", "interface", or even just "boundary" might be used.
The wave is called a "reflected wave" when it bounces back off the boundary between two different materials.
A wave that separates two different media is called a boundary or interface wave. Examples include reflection and refraction at the interface between two materials.
Reflection.
Light refracts when is crosses the boundary between two materials. That means that is the light is coming in at one angle, then it will change direction at the interface and have a different angle moving out from the other side. There is an old formula called Snell's Law that predicts the exit angle in terms of the properties of the material, i.e. in terms of the index of refraction. There is reflection as well. Some light bounces off of a boundary and some is transmitted.
The boundary between two materials is called an interface.
The question is too vague for a definitive answer; depending on context, "surface", "interface", or even just "boundary" might be used.
The wave is called a "reflected wave" when it bounces back off the boundary between two different materials.
The boundary between the troposphere and the stratosphere is called the tropopause.
Such a boundary is called a front.
The boundary between the Earth's crust and the upper mantle is called the Mohorovičić discontinuity, commonly referred to as the "Moho." This boundary marks a transition from the relatively rigid and lighter materials of the crust to the denser, more ductile materials of the upper mantle. The Moho is significant in geophysics and geology, as it helps to understand the composition and behavior of the Earth's interior.
The boundary of mantle and core are called Gutenberg Discontinuity
A boundary where the plates are moving apart is called a divergent boundary. It is also called a constructive boundary because new crust is made there.
A front
It is called a fault
A front
The boarder between two plates is called a boundary.