HTTP/2
The 2015 binary, multiplexed evolution of HTTP/1.1 that lets a single TCP connection carry many concurrent requests.
HTTP/2 (RFC 9113) replaces HTTP/1.1's text-based, head-of-line-blocked transport with a binary framing layer that multiplexes many request/response streams over one TCP connection. Headers are compressed with HPACK, servers can push resources proactively, and stream priorities hint at importance. Browsers only negotiate HTTP/2 over TLS, using ALPN to agree on `h2` during the TLS handshake. HTTP/2 dramatically improved page load times for resource-heavy sites and is still the dominant HTTP version on the web, with HTTP/3 (over QUIC) layered on top for the next jump.