The distance in pitch between two tones is known as an Interval.
interval
The question doesn't make any sense. If you want to know what the distance between pixels is called, it is dot pitch. If you are asking what the actual distance is, that depends on the monitor. The manufacturer would have this information.
It's called the range of the voice or instrument.
Yes, the x-distance, y-distance, z-distance, or any combination of the three between any two points may be zero Not possible. If the distance between two points is zero then the points are the same.
Wavelength
wavelength
wavelength
That is the wavelength.
wavelength
That's a description of "wavelength".
That is the wavelength.
Wavelength