D-subminiature

D-subminiature connectors are electrical connectors with a D-shaped metal shell that guides mating, prevents incorrect orientation, and can shield their contacts. Common variants include DE-9, DA-15, DB-25, and high-density forms.

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Connector (electronics): A device that joins electrical conductors to form a separable circuit connection. D-subminiature is one standardized family within the wider range of electrical connectors.
RS-232: A serial communication standard defining electrical signaling and interface characteristics. DE-9 and DB-25 connectors became familiar physical interfaces for RS-232 equipment.
Electromagnetic shielding: The reduction of electromagnetic interference by conductive or magnetic barriers. A conductive D-shaped shell can shield contacts and provide a path for interference currents.
Mini-DIN connector: A compact circular connector family with keyed shell and pin arrangements. Mini-DIN connectors offered a smaller alternative for keyboard, mouse, and video interfaces.
Cannon (company): An American connector manufacturer whose Cannon D series established the D-subminiature design. The connector family originated in Cannon’s product line before its name became widely generic.
Electrical contact: A conductive interface that transfers electrical current or signals between components. The shell surrounds the contacts that carry signals between the two mating halves.
VGA connector: A 15-contact analog video connector commonly arranged in three rows. The DE-15 D-sub is widely known as the VGA connector.
Shell (connector): The outer housing of a connector that supports and protects its contacts. The metal shell supplies the characteristic D shape and helps align mating halves.
HDMI: A digital interface standard for transmitting audio and video between devices. HDMI displaced analog D-sub video connections in many consumer displays.
D-subminiature nomenclature: The naming system combining shell-size letters with contact-count codes for D-sub connectors. The nomenclature explains why DB-25 is common shorthand although its shell designation is technically different.