Conventional/received wisdom noun phrase
General knowledge is accepted by the public.
The received wisdom has it that give a man a fish and you feed him for a day, but teach a man to fish and he'll eat forever.
The conventional wisdom is that if the dragonfly flies high it will be sunny, and if it flies low there will be rain.
The expression is often recorded to the economist John Kenneth Galbraith, who used it in his book The Affluent Society in 1958.
Completely dark, without any light or color
I'm scared of the basement! It's as black as a skillet!