Hypertext Transfer Protocol (HTTP) is a communication protocol used to transfer or convey information on the World Wide Web. Every HTTP server program operates by accepting HTTP requests from the network, and providing an HTTP response to the requester. The HTTP response typically consists of an HTML document, but can also be a raw text file, an image, or some other type of document; if something bad is found in client request or while trying to serve the request, an HTTP server has to send an error response which may include some custom HTML or text messages to better explain the problem to end users.

HTTP traffic is very insecure, all data is transferred in clear text; for this reason it was developed HTTPS (Hyper Text Transfer Protocol Secure), a secure version of the HTTP. HTTPS isn't a separate protocol, but refers to the combination of a normal HTTP interaction over an encrypted Secure Sockets Layer (SSL) or Transport Layer Security (TLS) transport mechanism based on digital certificates. Most typically HTTP data is sent over TCP/IP port 80, whereas SSL HTTP data is sent over port 443.