That is The Bass Rock, or simply the Bass, is an island in the outer part of the Firth of Forth. It’s on of a chain of volcanic plugs running in an east - west line across the ‘waist’ of Scotland.
Never heard it referred to as the “waist” of Scotland, but it makes perfect sense.
Tthe tallest mountain in the UK is at the west end of that waist, near fort something or other. It’s where I proposed to my wife!