What is HTTPS?
From Wikipedia.org "Hypertext Transfer Protocol Secure (HTTPS) is an extension of the Hypertext Transfer Protocol (HTTP). It is used for secure communication over a computer network, and is widely used on the Internet.".
So to say, it means that the data you are sending over the HTTP protocol are secured.
So as me, you are probably not understanding a thing about what it means. As it is all about security here, we are going to show the attack that hackers can perform when you are using website using HTTP only and not HTTPS.
This attack is often named as MITM, which is the acronym for Man In The middle. It consists of a person who is listening the interactions between you and the network (the network being often the internet).