This cable connects a newer, 24-pin ATX (version 2.x) power supply to an older, 20-pin ATX (version 1.x) motherboard power connector. This has a 24-pin male ATX 2.x connector and a 20-pin female ATX 1.x connector.
Note: It is important to remember that the gender of a connector is determined by the electrical connection itself, not the housing, casing, or shell. In most cases, the power source will use a female connector, just like that found in a typical wall socket. Therefore, the connector on the power supply cable will have female sockets and the connector on the motherboard will have male pins. The outside casing has no relation the gender of an electrical connector.