Measurements are all about precision, but the terms "dash", "pinch" and "smidgen" have always been a little vague. They do, however, have somewhat precise definitions, which can be helpful to know if you're scaling up a recipe.
Traditionally, a "pinch" simply meant the amount you could literally pinch between your forefinger and thumb, which usually falls somewhere between 1/16 and 1/8 of a teaspoon. A smidgen is half a pinch (1/32 of a teaspoon) and a dash is a liquid measurement that translates to to 1/8 of a teaspoon.
These terms are handy to know, but don't fret if you have tiny measuring spoons; these units are most commonly used for seasoning, so it's very unlikely you'll ruin anything by playing a little fast and loose with these amounts.