Next to my plug switches theres a socket which have a dimmer switch and somewhat hole... What is this? Its next to the mundane plug socket thus NOT next to...

Its next to the mundane plug socket thus NOT next to a wispy switch, so it is not a dimmer switch for the lights --- The hole is as big as a whole for some headset.
Water Problem In Garage?
Answers:    I'm just trying to have a handle on what you're describing.
So you have a wall plate (2-wide),nearby is a knob you can turn
on one side and just a 3/8", or 1/2" hole on the other?

It sounds similar to it MAY be something that "aimed" a roof antenna, and the wire to the TV enter through the whole.

You could try removing the plate, if at hand is electrical wires in it; it be probably for control of something.
Can solid rainfall lead to a backup surrounded...
This is probably a rheostat control for an electrical heater the hole is where on earth the cable for the heater go.

this is to allow for a variable output on a electric radiant furnace or radiator.