What does Serial Server mean?
A serial server is a networking device that transfers data between an Ethernet local area network and a computer's or a device's serial port (COM port). The main purpose of a serial server is to allow a serial device such as a printer, scanner or climate control system to be used in a network without relying on the serial port of a computer for connectivity. This allows any serial device to be connected to the network and accessed from anywhere, including from the Internet.
Serial servers are also known as serial port servers or port redirectors.
Techopedia explains Serial Server
A serial server is basically a server that transforms any serial device into an Ethernet-capable device that can be used in a network. For example, an old non-network-capable printer that would traditionally only work when attached to a computer's COM port can be transformed into a networked printer and controlled from anywhere by attaching it to a serial server, which, in turn, is connected to the network through Ethernet cables. This is achieved by the serial server through the creation of virtual serial ports (which have actual serial port connector hardware, only the interface is virtual) that mimic the port of the PC, tricking the device into thinking that it is connected to one. The serial server makes the necessary assignment of IP address and TCP ports to the virtual serial port so that devices and users can communicate with the serial device attached to the server, as well as route traffic to the correct serial device.
A serial server can be a very simple device that does not offer any authentication and security, and is there simply to connect the serial device to the network, or it can be a complex device that offers many functionalities similar to that of Ethernet switches and routers. Devices with no security or authentication are used in situations where data and access to serial devices are not a security issue, such as in local office scenarios involving a printer. By contrast, more sophisticated serial servers with full encryption and multiple authentication are used in sensitive situations where security is important, such as remotely controlling critical systems like environment control systems, factory control mechanisms and other industrial applications where safety is paramount.
Depending on the model, a serial server can interface with simple printers, large-format screens, robotic assembly machines, medical equipment, sensors and other industrial equipment that originally could only interface through the serial port.