HTTP stands for Hypertext Transfer Protocol.
HTTP is used as the main protocol of the internet. It runs on top of TCP and enables web browsers and other applications to connect and interact with web servers.
HTTP is a client-server protocol where the web browser is considered the client. In HTTP, only the client can send a request to the server and the server can only offer a response.
HTTP has evolved a bit through the years, growing and updating with the changes of the web. The current version used is HTTP/1.1, which has a wide deployment throughout the internet. It is considered to be inefficient. There are talks and discussions today about updating it to HTTP 2.0, based on SPDY.
HTTP has a secure variant of it called HTTPS.