HTTP is Hyper Text Transfer Protocol. You see the letters of http appear in the address bar sometimes and sometimes web addresses use them also.
A protocol is a set of rules that two devices use to be able to communicate with each other. HTTP is a protocol that is used to send web pages from the server to your PC.
The language that web pages are developed in is quite often HTML (HyperText Markup Language. You may wonder what hypertext is since it is part of the name of the language and the protocol. Hypertext says that pages have links in the text (or images) on the page that when clicked take you to another web page.
The HTTP protocol tells the server and PC how to send each other directions on what web page to send to teh PC and how the web p[age is received by the PC so it can display it so we (humans ) can understand what is on the page.
We as humans use various protocols in life also. For instance it is normally protocol (not law) that tells us to walk on the right side of halls. Protocol also says you don't leave your foot stuck out so someone trips on it. Protocol says that we as Americans are to bow for the queen of Great Britain but not kneel.
There are lots of other protocols used on the Internet. Another two you may see sometimes are SMTP which is the protocol to send e-mails and FTP which is used to move a file from one to computer to another cross a network or the Internet.