D-sub connectors are a type of electrical connector commonly used for data and video transmission. They feature a D-shaped metal shell that provides a secure connection and helps prevent incorrect insertion. These connectors come in various sizes and pin configurations, making them suitable for different applications, such as computer interfaces and industrial equipment. The most well-known variant is the DB-25, which has 25 pins and is often used for parallel ports and serial connections. Other types include DE-9 and DA-15, which are used for different purposes, including RS-232 serial communication and VGA video connections, respectively.