A telnet to a server
Most of the time people check connectivity via
telnet <ip-address> <port-number> telnet <name-of-the-server> <port-number>
But ping command listens on other ports than you expect. Hence, you might get response back from server but in reality when you try to send request to the server you might not get response back.
Hence, telnet test is more reliable compare to ping test.