HTTP/2 (RFC 7540) changed on-the-wire format of HTTP from a simple text-based request and response headers to binary data format sent in frames. HTTP/2 supports compression of the headers (HPACK).
This reduced overhead of requests, and enabled receiving of multiple responses simultaneously over a single TCP/IP connection.
Despite big changes in the data format, HTTP/2 still uses HTTP headers, and requests and responses can be accurately translated between HTTP/1.1 and 2.