Server push

The server can push data to the client. When the client requests data from the server, the server can figure out that the client will need some other data as well. The server can push this data to the client. The client can always reject the data by signaling to the server that push data should be disabled. This data sent by the server to the client is called a PUSH_PROMISE frame. The data is stored in the client's cache if it implements an HTTP cache.