"Bioavailability (F) is defined as the rate and extent to which the active constituent or active moiety of a drug is absorbed from a drug product and reaches the circulation."
https://www.sciencedirect.com/topics/medicine-and-dentistry/bioavailability
"the degree and rate at which a substance (such as a drug) is absorbed into a living system or is made available at the site of physiological activity"
https://www.merriam-webster.com/dictionary/bioavailability
"The bioavailability of a substance can fluctuate, depending on the route of administration. Intravenous administration, or a direct line into the bloodstream, is typically considered 100% bioavailability, as all of the substance will reach target cells. In oral administration routes, AKA when you take a pill, the amount of medicine or supplement you receive depends on many factors, including your diet and your personal metabolism.
Bioavailability has become a new and upcoming science in recent decades."
https://biologydictionary.net/bioavailability/