Superfecundation is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse. The term superfecundation is derived from fecund, meaning the ability to produce offspring. Heteropaternal superfecundation occurs when two different males father fraternal twins. In common usage, the term superfecundation is often used instead of heteropaternal superfecundation. The terms are practically equivalent because, though superfecundation by the same father is thought to be a common occurrence, it can only be proven to have occurred with multiple fathers.