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The word "protocol" is a fancy way of saying "communication method that computer people have all agreed to use." For instance, you could think of human languages as protocols. People that speak English to one another have agreed to use that communications method to get things done, but if you don't speak English, then you can't communicate with those that do.
When you use the Web, you're using a protocol called "HTTP," which explains why all your web addresses start with "http://"—you're letting your computer and your web browser know that you want to use the HTTP protocol to communicate, to access a web page.
Likewise, when you send an email, you're using a protocol called "SMTP," which stands for Simple Mail Transfer Protocol. You probably don't even realize that you're using it, which is a good thing, since it allows you to communicate without having to worry about the plumbing.
There are lots of other protocols for doing various things on the Internet, but they all serve to make communication between programs that use those protocols easier and more efficient, as well as possible in the first place!
The word 'protocol' comes from the diplomatic service and simply means an agreed way of carrying out a deal. When you go to a store to buy something, the agreed method is usually quite simple. I put a price on the object, you agree to the price by paying it, and in exchange I give you the object. When you hear a conversation between a control tower and an airplane you might here the word 'over' which is a short way of saying -"I have finished speaking, now it is your turn". Or they may say 'out' which means "goodbye, I am ending this conversation". They have an established protocol. Now, if you hear two people arguing where neither stops to hear what the other is saying then we call that a "breakdown in communication".