Culinary definition of pinch: The amount of ingredient that can be picked up and held between thumb and forefinger.
C@H FOOD FOR THOUGHT
A pinch is a unit-of-measurement reference, like tablespoon or litre, used in recipes. Pinches of salt and pepper are commonly recommended, though chili flakes, dried herbs and spices, and sugar are added to recipes in 'pinches' as well.
Conventional wisdom says that a pinch of regular table salt shouldn't be larger than 1/8 of a teaspoon (< 1 gram), so using this as a reference you can better estimate when recipes call for a 'generous pinch' or a 'wee pinch'.