A very small amount of something, a tiny bit or pinch.
Origin uncertain, but possibly related to 'smutch' (a stain or smudge). Used in American English from the early 1900s as informal slang for a small quantity.
Recipes that call for 'just a smidge' of salt show how powerful tiny amounts can be—one smidge too much can completely ruin a dish!
Complete word intelligence in one call. Free tier — 50 lookups/day.