Glossary

HTTP/2

HTTP/2 is the second major version of the HTTP protocol, adopted in 2015. It solves the key problems of HTTP/1.1: head-of-line blocking and the overhead of opening new connections.

Key improvements

Multiplexing — multiple requests and responses simultaneously over a single TCP connection. The end of the browser's "6 parallel connections" limit
Server Push — the server can send a resource before the client has requested it
Header Compression (HPACK) — headers are compressed and repeated only when changed
Binary protocol — replaces the text-based format; more efficient to parse

HTTP/3

The next step — HTTP/3 over QUIC (UDP instead of TCP). Solves head-of-line blocking at the transport layer. Supported by browsers and CDNs, but requires specific server configuration.