What is "serial"

The serial interface or serial port, also known as RS-232 is a communication port used to connect pendrives, modems, mice, some printers, scanners and other hardware equipment.

In the serial interface, the bits are transferred in queue, that is, one bit of data at a time. The RS-232 standard was originally set for communication over 25 different wires. IBM, by using the standard for its IBM-PC design, defined that only 9 pins would be required. However, the DB25 connector was kept in the computers, because it is a standard of the time.