The HTTP/2 specification RFC 7540 was published in May 2015 and the protocol has since then been implemented and deployed widely across the Internet and the World Wide Web.
In early 2018, almost 40% of the top-1000 web sites run HTTP/2, around 70% of all HTTPS requests Firefox issues get HTTP/2 responses back and all major browsers, servers and proxies support it.
HTTP/2 addresses a whole slew of shortcomings in HTTP/1 and with the introduction of the second version of HTTP users can stop using a bunch of work-arounds. Some of which are pretty burdensome on web developers.
One of the primary features of HTTP/2 is that it makes use of multiplexing, so that many logical streams are sent over the same physical TCP connection. This makes a lot of things better and faster. It makes congestion control work much better, it lets users use TCP much better and thus properly saturate the bandwidth, makes the TCP connections more long-lived - which is good so that they get up to full speed more frequently than before. Header compression makes it use less bandwidth.
With HTTP/2, browsers typically use one TCP connection to each host instead of the previous six. In fact, connection coalescing and "desharding" techniques used with HTTP/2 may actually even reduce the number of connections much more than so.
HTTP/2 fixed the HTTP head of line blocking problem, where clients had to wait for the first request in line to finish before the next one could go out.