The phenomenon describing the increase in the frequency of a wave as its source moves closer is known as the Doppler effect. This effect occurs in various contexts, such as sound waves and electromagnetic waves (light). As the source approaches an observer, the waves are compressed, resulting in a higher frequency or pitch. Conversely, as the source moves away, the waves are stretched, leading to a lower frequency. The Doppler effect is leveraged in applications such as radar and astrophysics to measure velocities of objects.