A generic drug (short: generics) is a drug which is produced and distributed without patent protection. A generic must contain the same active ingredients as the original formulation. In most cases, it is considered bioequivalent to the brand name counterpart with respect to pharmacokinetic and pharmacodynamic properties. By extension, therefore, generics are assumed to be identical in dose, strength, route of administration, safety, efficacy, and intended use. In most cases, generic products are not available until the patent protections afforded to the original developer have expired. When generic products become available, the market competition often leads to substantially lower prices for both the original brand name product and the generic forms. The time it takes a generic drug to appear on the market varies. Drug patents give twenty years of protection, but they are applied for before clinical trials begin, so the effective life of a drug patent tends to be between seven and twelve years.

http://en.wikipedia.org/wiki/Generic_drug