RFC 7540 - Hypertext Transfer Protocol Version 2 (HTTP/2) https://tools.ietf.org/html/rfc7540#page-4
The Hypertext Transfer Protocol (HTTP) is a wildly successful protocol. However, the way HTTP/1.1 uses the underlying transport ([RFC7230], Section 6) has several characteristics that have a negative overall effect on application performance today. In particular, HTTP/1.0 allowed only one request to be outstanding at a time on a given TCP connection. HTTP/1.1 added request pipelining, but this only partially addressed request concurrency and still suffers from head-of-line blocking. Therefore, HTTP/1.0 and HTTP/1.1 clients that need to make many requests use multiple connections to a server in order to achieve concurrency and thereby reduce latency. Furthermore, HTTP header fields are often repetitive and verbose, causing unnecessary network traffic as well as causing the initial TCP [TCP] congestion window to quickly fill. This can result in excessive latency when multiple requests are made on a new TCP connection. HTTP/2 addresses these issues by defining an optimized mapping of HTTP's semantics to an underlying connection. Specifically, it allows interleaving of request and response messages on the same connection and uses an efficient coding for HTTP header fields. It also allows prioritization of requests, letting more important requests complete more quickly, further improving performance. Belshe, et al. Standards Track [Page 4]
RFC 7540 HTTP/2 May 2015 The resulting protocol is more friendly to the network because fewer TCP connections can be used in comparison to HTTP/1.x. This means less competition with other flows and longer-lived connections, which in turn lead to better utilization of available network capacity. Finally, HTTP/2 also enables more efficient processing of messages through use of binary message framing.
HTTP 2.0_百度百科 https://baike.baidu.com/item/HTTP%202.0/12520156
2.2 HTTP复用：HTTP/2.0提供了在单个连接上复用HTTP请求和响应的能力。 多个请求或响应可以同时在一个连接上使用流（发送第5节 ）。 为了保持独立的流，流控制和优先级是必要的。