How is the relationship between bioavailability and bioequivalence of a drug?

Bioavailability is: the fraction of the administered dose of a drug that reaches the bloodstream. For example, if you swallow a 10mg tablet of drug X, and 5mg gets to the bloodstream, it has 50% bioavailability. Bioavailability of IV administered drugs is 100% by definition. Bioequivalence is used to assess the biological equivalence of two preparations of the same drug, for example a generic and brand name drug.