HTTP/2 is the first major HTTP protocol update since 1997 when HTTP/1.1 was first published by the IETF. The new HTTP protocol is needed to keep up with the exponential growth of the web. HTTP/2 brings significant improvement in efficiency, speed and security. The speed advantage to your site is 50% to 70% faster using HTTP/2. source: keycdn.com
• HTTP/2 is binary, instead of textual.
• It is fully multiplexed, sending multiple requests in parallel over a single TCP connection.
• It uses header compression HPACK to reduce overhead.
• It allows servers to "push" responses proactively into client caches instead of waiting for a new request for each resource.
• It uses the new ALPN extension which allows for faster-encrypted connections since the application protocol is determined during the initial connection.
• It reduces additional round trip times (RTT), making your website load faster without any optimization.
• Domain sharding and asset concatenation is no longer needed with HTTP/2.
• Most modern web browsers support HTTP/2 but only on sites using HTTPS protocol.
To test if your server supports HTTP/2 you can use this tool