In HTTP/1 the server can send a header “Connection: Keep-Alive” to tell the client that it doesn’t have to close the socket after receiving the reply, and can s

In HTTP/1 the server can send a header “Connection: Keep-Alive” to tell the client that it doesn’t have to close the socket after receiving the reply, and can send another request. (HTTP/2+ have this built into the wire protocol and don’t need the header.) If the browser doesn’t have another request to send immediately, it will still keep the connection in a “socket pool” for a while in case it needs to make another request to the server later.