Ingredient substitution refers to the practice of replacing one ingredient in a recipe with another that serves a similar purpose. This can be useful for accommodating dietary restrictions, using what you have on hand, or enhancing flavors. For example, if a recipe calls for buttermilk, you can substitute it with a mixture of milk and vinegar or lemon juice. When substituting ingredients, it's important to consider the texture, flavor, and cooking properties of the alternatives. For instance, if you need to replace eggs in a baking recipe, options like applesauce or flaxseed meal can work well. Understanding these substitutions can help ensure successful cooking and baking outcomes.