A serial port is a type of interface used for communication between a computer and external devices, such as printers, modems, or mice. It transmits data one bit at a time over a single wire, making it different from parallel ports, which send multiple bits simultaneously. Serial ports are commonly found on older computers and are often used for connecting devices that require simple, low-speed data transfer. Typically, serial ports use a standard connector called a DB9 or DB25, which has 9 or 25 pins, respectively. They operate using protocols like RS-232, which defines the electrical characteristics and timing of the signals. Although less common today due to advancements in technology, serial ports are still used in various applications, including industrial equipment and embedded systems.