You used the correct term - bioavailability describes the fraction of a drug dosage that can enters the bloodstream.
Your example however makes an incorrect assumption. Bioavailability from snorting a powdered drug is higher than oral ingestion. When snorted, the drug passes through the thin lining of the nose and enters the bloodstream directly. When ingested orally, the drug has to make it through the chaos of the stomach and small intestine, get through the hepatic pathway (stomach and intestinal lining to liver to general bloodstream) before it reaches the rest of the body.
Your example however makes an incorrect assumption. Bioavailability from snorting a powdered drug is higher than oral ingestion. When snorted, the drug passes through the thin lining of the nose and enters the bloodstream directly. When ingested orally, the drug has to make it through the chaos of the stomach and small intestine, get through the hepatic pathway (stomach and intestinal lining to liver to general bloodstream) before it reaches the rest of the body.