It is a serial communication port, or serial port for short.

Ports can be categorized into virtual ports and physical ports, where virtual ports refer to ports inside a computer or inside a switch router that are not visible. Hardware ports: The CPU transfers data to and from peripherals through interface registers or specific circuits, which are called ports. The ports in the hardware area are also known as interfaces, e.g., parallel ports, serial ports, and so on.

Network Ports: In network technology, port (Port) has several meanings, the port of hubs, switches, routers refers to the interface that connects to other network devices, such as RJ-45 ports, Serial ports and so on. The port referred to here does not mean the physical sense of the port, but specifically refers to the TCP/IP protocol port, is the logical sense of the port.

Expanded Information:

On the Internet, hosts send and receive packets via the TCP/IP protocol, and each packet is routed according to the ip address of the destination host, so that the packet is successfully delivered to the destination host. Most operating systems support multiple programs (processes) running at the same time, so the destination host should transmit the received packets to which of the many processes running at the same time? Obviously, this is a problem that needs to be solved, and this is where the port mechanism is introduced.

The local operating system assigns protocol ports to those processes that need them, each identified by a positive integer, such as 80, 139, 445, and so on. When the destination host receives the packet, it will send the data to the corresponding port according to the destination port number at the beginning of the message, and the process corresponding to this port will receive the data and wait for the next set of data to arrive. At this point, the concept of ports still seems abstract, so continue with me and don't go away.