Master Ingredients is your ingredient library. It holds every ingredient you have used across your recipes and lists, in one place, so the same thing is named and sorted the same way everywhere it shows up.
Search the library to jump to any ingredient. As your collection grows, search is the fastest way to land on the one you want to edit or add to a list.
A few tools keep the library clean:
Cleaning up here pays off on your grocery list, where folded and merged ingredients combine into single lines instead of scattering.
You can set a default store and aisle for each ingredient. That tells Tradish where an item usually lives, so when it shows up on your grocery list it drops into the right aisle at the right store automatically. To set up those stores and aisles first, see Stores and aisle sections.
Need something that is not tied to a recipe or a plan? You can quick-add an ingredient straight from the library to your grocery list. It is a fast way to catch the odd item, like foil or dish soap, without opening a recipe.