A print server is a device that allows you to share a printer with multiple computers. It may be a standalone adapter or may be integrated within a printer or a router. When activated, the print server allows a printer to connect to a local network rather than a single computer. The printer can then be accessed by multiple devices (including both Mac and Windows computers) as a "network printer."
Standalone print servers come in several varieties. Most have a USB port, which connects directly to the USB port of the printer. However, some print servers can connect to a printer's Ethernet or parallel port as well. Wired print servers include an Ethernet port for connecting directly to a router, while wireless versions are able to connect to a Wi-Fi network.
Printers that include a built-in print server are often called "network printers" or "wireless printers." These printers may have an Ethernet port for connecting directly to a LAN or a built-in Wi-Fi card, which enables the printer to show up on a wireless network. Since many homes and businesses now have wireless networks, wireless printers have become a popular way to share a printer with multiple computers.
Some routers can also function as print servers. Besides the typical Ethernet ports, they also include a USB port for connecting a printer. When you connect a printer to the router, the printer becomes a network device and can be accessed by other devices on the network.