In electrical and mechanical trades and manufacturing, each of a pair of mating connectors or fasteners is conventionally assigned the designation male or female. The assignment is by direct analogy with animal genitalia; the part bearing one or more protrusions, or which fits inside the other, being designated male and the part containing the corresponding indentations or fitting outside the other being female.

In contexts where alternatives to the terms male and female are desired, "socket", "receptacle", "outlet" and "jack" are used for female connectors, and "plug" for male connectors. In many cases these terms are more common than male and female, especially in documentation intended for the non-specialist.

In electrical connections where voltage is sufficient to cause injury, the part connected to the power source is invariably female, so that hazardous voltage is not exposed to inadvertent contact. A plug is connected to the device drawing the power. Personal computers and their monitors are a special case, with a socket on the device end which fits in a space on the back of the device for stability and to prevent inadvertent disconnection.

In low-voltage use, such as for data communications, this is less important, and male or female connectors are used based on other engineering factors such as convenience of use or ease of manufacturing. For example, the common "patch cables" used for Ethernet hookups (and the similar cords used for telephones) typically have plugs on both ends, to connect to jacks on equipment or mounted in walls. A device called a gender changer may be used to join two connectors of the same gender, for example, to extend one video cable with another.

The gender of a connector is determined by the structure of its primary functional components—i.e., the conductors of an electrical connector, or the load-bearing parts of a fastener—and not by secondary features such as covers, shields or handles that may be installed for environmental protection, safe operation, etc.

Certain connector designs involve paired identical parts each containing both protrusions and indentations. The term hermaphrodite (or hermaphroditic) is used for such devices, along with combination (and combo), two-in-one, two-way, and others.

Examples

• A power cord on a lamp or appliance terminates in a (male) plug; it connects to a (female) socket in a wall or on an extension cord.
• Co-axial cables used for video or other high-frequency signals are normally terminated, at both ends, in a connector comprising an inner pin and an outer fixed or rotating shell; these are conventionally reckoned as male.
• A nut is female and a bolt is male.