Boundary or interface.
The boundary between two sedimentary rock layers is called a bedding plane or stratigraphic boundary. It represents a break in the deposition of sediment, marking a change in the environment or conditions under which the rocks were formed.
The boundary between two plates moving together is called a convergent boundary. At convergent boundaries, one plate is usually subducted beneath the other, leading to the formation of mountain ranges, deep ocean trenches, and volcanic activity.
When two tectonic plates slide past each other horizontally, the boundary between them is called a transform boundary. This type of boundary is characterized by lateral movement along fault lines, such as the San Andreas Fault in California.
It is called seismic wave reflection. When a seismic wave encounters a boundary between different materials with contrasting density or rigidity, some of the wave energy is reflected back towards the source.
A front
The boundary between two materials relating to light is called a interface. This is where light rays can be reflected, refracted, or absorbed as they pass from one material to another.
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.
Surface Wave (APEX)
A front
The boundary between two zodiac signs is called a cusp. When someone is born close to the transition between two signs, they may exhibit traits from both signs.
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.
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The boarder between two plates is called a boundary.
When an ultrasound wave reaches a boundary between two different materials, some of the wave gets reflected back, while some of it gets transmitted into the new material where it may be absorbed or refracted. The amount of reflection and transmission depends on the acoustic impedance mismatch between the two materials.
contact
The boundary between two sedimentary rock layers is called a bedding plane or stratigraphic boundary. It represents a break in the deposition of sediment, marking a change in the environment or conditions under which the rocks were formed.