In the context of waves, the term "rest position" refers to the equilibrium or undisturbed state of the medium through which the wave propagates. It is the position where the particles or elements of the medium are at their equilibrium positions, unaffected by the wave passing through.
In a transverse wave, such as a wave on a string or an electromagnetic wave, the rest position represents the position of the medium when it is not experiencing any displacement due to the wave. For example, in the case of a wave on a string, when the wave is not present or is at a point where the displacement is zero, the string is at its rest position.
In a longitudinal wave, such as a sound wave, the rest position refers to the position where the particles of the medium are in their natural, undisturbed state. When the sound wave passes through the medium, the particles oscillate back and forth around their rest positions.
It's important to note that the concept of rest position may vary depending on the type of wave and the medium through which it propagates. In general, it represents the equilibrium state of the medium before the wave passes through, where there is no net displacement or disturbance caused by the wave.