Hypertext Transfer Protocol is the application-layer protocol that powers the web. HTTP defines how clients (browsers, applications, AI agents) request resources from servers and how servers respond. The modern web runs on HTTP/1.1 (introduced 1997), HTTP/2 (2015), and HTTP/3 (2022), each successive version addressing specific performance limitations of its predecessor.
HTTP is the archetypal infrastructure protocol — it reached universal adoption in the 1990s, remained mostly invisible to end users, and became load-bearing for the entire commercial internet. Every enterprise API, every cloud service, every SaaS product runs over HTTP in some form.
In modern enterprise deployment, unencrypted HTTP has been largely replaced by HTTPS (HTTP over TLS). Plain HTTP is still used for internal services on trusted networks but is a security anti- pattern for anything touching the public internet. "HTTP" in casual usage almost always refers to HTTPS in practice.