Fluid substitution refers to the process of replacing one type of fluid with another in a given system, often to maintain balance or improve performance. This concept is commonly applied in various fields, including geophysics, where it helps in understanding subsurface properties by substituting fluids in rock formations. In medical contexts, fluid substitution can involve replacing lost bodily fluids, such as during dehydration or surgery. This is crucial for maintaining homeostasis and ensuring that the body's functions continue to operate effectively. Proper fluid management is essential for overall health and recovery.