Bile is a digestive fluid [a liquid that helps break down food] produced by the liver and stored in the gallbladder. It helps to break down fats in the small intestine and aids in the absorption of fat-soluble vitamins [vitamins that need fat to be absorbed in the body]. For example, when you eat a slice of pizza, bile is released to help digest the cheese and other fatty components.
Very Simple Definition:
Bile is a liquid that helps our body digest fatty foods. Our liver makes it and stores it in the gallbladder until we need it. When we eat pizza or other fatty foods, bile helps our stomach break it down so our body can use the nutrients.