TCP/IP is a group of network protocols that enable communication and set standards for those communications between network devices. A LAN printer, is simply a network printer, which is a printer that simply has a network card, like a PC. I'm not sure where you seen the description of a TCP/IP printer, but they probably meant a network printer. In this case, they are more than likely the same.
A print server basically sets between a computer and a printer on a network, and distributes print jobs to the specified printers from whatever application the user is printing from. This looks like some good reading.... http://en.wikipedia.org/wiki/Print_server
