Modular connectors have gender: male connectors are called plugs, while female connectors are called jack or, sometimes, sockets. Modular connector were originally used in telephone wiring. Even though they are still used for that purpose they are used for a variety of other things as well. A modular connector's advantage over many other kinds include small size and ease of plugging and unplugging.

Modular connectors come in four size: 4-, 6-, 8-, and 10-position, where a position is a location for a contact. Not all of the positions may have contacts: when contacts are omitted, they are typically done so from the outermost two contacts inward, such that the number of contacts is always an even number.