We have a vague general idea of what that means but there are significant local variations based on people's personal nature.
There are plenty of people with a few million who'll skulk around the harbour at Cannes and not think of themselves as rich.
I don't think of myself as rich but if someone had shown the 18 year old me my P60 for last year I imagine my eye's would have been as round as dinner plates
I honestly don't think you can just put a number on it because it also depends on the cost of living. My aunt's boyfriend and his brother both earn roughly the same. The brother has a job that allows him to work from home so he moved to a cheap area of the country and owns a lovely house and car. The aunt's boyfriend has a job which requires him to be in London and he rents a small flat and can't afford a car.