HTTP stands for Hypertext Transfer Protocol. It is the foundation of data communication on the World Wide Web, facilitating the transfer of hypertext documents, which can contain text, images, and links. This application-layer protocol defines how messages are formatted and transmitted, allowing web browsers and servers to communicate. Major versions of HTTP include HTTP/1.1 and HTTP/2, with the latter providing improved performance through multiplexing and header compression. The transition to HTTPS, which adds an extra layer of security through SSL/TLS, enhances data privacy during transmission.