A client is a computer program that talks to a server . A server provides 'useful' information. A client gets 'useful' information. They talk to each other using a special protocol . A protocol is a way of exchanging information over the net.
Gopher is a 'browser' for gopher sites, wais sites, and ftp sites.
It also provides 'gateways' to telnet sites. A gateway is when one program runs another program. Gopher can 'run' telnet, but you are then in telnet, rather than gopher, and you don't have the gopher menus. You are 'dropped back' into gopher when you leave the telnet session. Gopher is not just a set of ftp sites.