Fluxes refer to the rate of flow of a property per unit area. In physics and engineering, this concept is often used to describe how quantities like energy, mass, or momentum move through a surface. For example, in electromagnetism, the flux of an electric field through a surface can indicate how much electric field lines pass through that area. In environmental science, fluxes can describe the movement of substances like carbon dioxide or water between different reservoirs, such as the atmosphere, oceans, and land. Understanding these fluxes is crucial for studying processes like climate change and ecosystem dynamics, as they help quantify how materials cycle through the environment.