Bioavailability refers to the extent and rate at which a substance, such as a nutrient or drug, is available for absorption by the body. In other words, it measures how effectively a compound can be utilized by the biological system after being administered. The term often used in pharmacology when describing the efficiency of a medication to produce its desired effect once ingested. A high bioavailability means that the substance is easily absorbed and reaches the target site within the body, while low bioavailability indicates limited accessibility or slow uptake by the system. Factors such as formulation, route of administration, and individual physiological differences can influence a compound's bioavailability.