So we've just moved in to a new home. (Renting)
Guessing the ex tenants put this in the wall, at about 1 metre high.
Had no idea what it was. Poked fingers in, nothing behind it. Size of a power point.
After googling, you put one behind a wall mounted telly, and another at floor level, and run the telly power and cables through it.
Great idea. Except it is in the master bedroom, and there's only one of them.
A wall hole to nowhere, for no reason.