Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection. – Wikipedia
If you don't have telnet installed, install it with this following terminal command:
sudo apt install telnet
How to use
Enter the following lines into terminal
telnet robkjohnson.com 80
GET / HTTP/1.1
What is returned is essentially plain text of the source code. Which is exactly what your browser receives through the same GET/HTTP1.0 or GET/HTTP1.1 request.
Telnet is an old protocol that does not have any security, so anyone can eavesdrop on your connection. So make sure you're not accessing anything private with it.
Thanks goes to @xunker for teaching me this.