HTTP/2 (RFC 7540, 2015) replaced HTTP/1.1's text-based framing with a binary framing layer + multiplexing: many requests can be in flight on the same TCP connection without head-of-line blocking. Header compression (HPACK) reduces request size dramatically when headers repeat. Server push (since deprecated by Chrome) let servers proactively send resources before the client requested them.
In practice, HTTP/2 ships almost universally over TLS (h2 protocol). Plain-HTTP HTTP/2 (h2c) is rarely seen. Browsers and CDNs negotiate h2 automatically via ALPN during the TLS handshake.
Performance impact: larger benefit on HTTPS-everywhere sites with many small resources; smaller benefit on sites that already use a CDN with HTTP/1.1 keep-alive + sharded domains. HTTP/3 (over QUIC) is the next evolution, addressing TCP head-of-line blocking with UDP-based transport.