This article is about ingredients in general. There is also an American soul and R&B group called The Main Ingredient.
Aningredient is something that forms part of a mixture (in a general sense). For example, in cooking, a recipe will specify which ingredients are used to prepare a specific dish. Many commercial products contain a secret ingredient that is purported to make them better than competing products. In the pharmaceutical industry, an active ingredient is that part of a formulation that yields the effect required by the customer.
Nationallaws usually require prepared food products to display a list of ingredients, and specifically require that certain additives be listed.