HTTP
HTTP, short for Hypertext Transfer Protocol, is the basic request-response protocol browsers and servers use to exchange web resources. In the simplest version of the story, a browser sends an HTTP request, a server sends back an HTTP response, and the browser then decides what to do with the returned resource.
That description is deliberately minimal, but it earns its place because it replaces magical language like "the site loads" with a visible sequence of events. A user enters a URL, the browser makes a request, the server answers, and the browser may then make more requests for stylesheets, scripts, images, fonts, or data before the page is fully rendered.
The core mental move is to see HTTP as language rather than magic. A request says what resource is being asked for and what action is intended. In beginner examples this is often a GET request such as GET /courses. The server responds with the requested resource plus status information that tells the client how to interpret the result.
HTTP is therefore less an isolated networking term than a core part of how the visible web actually works. It sits underneath websites, search engines, and most ordinary browsing, even when the user never notices it directly.
One reason the concept becomes practically useful quickly is that HTTP makes web success and failure legible through status codes. 200 means success. 301 means the resource moved. 400 means the request could not be processed as sent. 403 means forbidden. 404 means not found. 503 means the server is temporarily unable to handle the request. These codes are not mere trivia. They are the visible labels of different states in the request-response chain.