In an amplifier, a presence control boosts the upper mid-range frequencies to make the sounds of voices and instruments with similar tonal ranges seem more "present".
[1] On television production studio's sound desk, there can be several presence controls, for several different, switchable, frequencies.
[5] The original Fender presence control acted upon the amplifier's negative-feedback loop.
Increasing the presence resulted in there being less and less negative feedback on high frequencies.
It had the ability to both amplify (boost) and attenuate (cut), unlike the earlier presence control.