When a wave goes from one medium to another and changes speed and direction, it's called refraction.

Here's a breakdown:

* Speed Change: Waves travel at different speeds in different mediums. For example, light travels slower in water than in air. This change in speed causes the wave to bend.

* Direction Change: The bending of the wave due to the change in speed is called refraction. The angle of refraction depends on the angle of incidence (the angle at which the wave hits the boundary) and the indices of refraction of the two mediums.

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