Ash is the fine, powdery residue left after the combustion of organic materials, such as wood or paper. It consists mainly of minerals and can vary in color from gray to black, depending on the material burned. Ash is often used in gardening as a natural fertilizer, as it contains essential nutrients like potassium and calcium. In addition to its use in gardening, ash can also be a component in various industrial processes. For example, fly ash is a byproduct of burning coal in power plants and is commonly used in the production of concrete. This helps improve the strength and durability of the final product.