Ingredient substitutions are alternatives you can use in recipes when you don't have a specific item on hand. For example, if a recipe calls for buttermilk, you can mix milk with a little vinegar or lemon juice to create a similar tangy flavor. This allows you to continue cooking without needing to run to the store. Using substitutions can also cater to dietary restrictions or preferences. If someone is allergic to gluten, you can replace all-purpose flour with almond flour or coconut flour. These swaps help maintain the integrity of the dish while accommodating different needs.