Absorption is the process by which one substance takes in another substance. In biology, it often refers to how living organisms take in nutrients from their environment. For example, in the human body, the small intestine absorbs nutrients from digested food, allowing them to enter the bloodstream and nourish cells. In physics, absorption describes how materials take in energy, such as light or sound. When light hits a black surface, for instance, the surface absorbs most of the light energy, converting it into heat. This process is essential in various applications, including solar energy collection and soundproofing.