How am I able to telnet to HTTP port 80?

After searching in google I found out that we can telnet to web-server to its http port and use GET to retrieve a html page. For ex: $ telnet web-server-name 80 But I am not able to understand how is this possible ? I thought that if port 80 is for http server, then port 80 will only listen for http requests. But how am I able to telnet to an HTTP port ? Aren't telnet and HTTP two different protocol ?