It is called the action, which means the height/distance of the strings from the fretboard..
lengthThe distance between two points is called the displacement.
The shortest distance between any two points is called displacement.
This distance is called the diameter.
The distance in pitch between two musical notes is called an interval.
the distance between two adjacent compressions is called the wavelength
The wave length. This is also correct if you are referring to the distance between the trough of two waves.
Hamming Distance
The longest distance in a circle is its diameter.
That is simply called the "distance".
It is called the wavelength.
The nearest distance is called the perihelion and the furthest distance is called the aphelion (there is about 5 million km difference). The mean distance is called one astronomical unit.