A gender changer is a hardware device placed between two cable connectors of the same type and gender. An example is a cable connector shell with either two female or two male connectors on it (male-to-male or female-to-female), used to correct the mismatches that result when interconnecting two devices or cables with the same gender of connector.
Gender changers are used for RS-232C ports in either the original DB-25 or the IBM AT DE-9 format. They are also used when extending any sort of cable that normally has plugs on both ends (rather than a socket on one and plug on the other), however in this case it is usually called just an “extender”, such as with F connectors, BNC connectors, and various RJ connectors used in telephony and computer networking.
Gender changers are used in professional audio to adapt XLR connectors, RCA connectors, Speakon connectors and TRS connectors.