Ingredients are required by recipes to create food, drinks, medicine, and a variety of game items. They can come from plants, farm fields, animals, mining, special objects, fishing, crafted from other ingredients (the list is almost endless).
They are virtual goods, aren't send as objects to your Second Life inventory, and need to be stored into containers and storage units. When you harvest a farm field, for example, you will need a container rezed nearby for the field send the harvest to it to store. Even getting water from a well requires a container. Check the Containers section for more information.
Below a list of ingredients available in the game. The common source is the name of the object that produces the ingredient, but ingredients can be acquired in other forms.
You can also see this page alone: Ingredients List