How is server response speed calculated?

A

Anton Seredny2016-03-01 16:08:15

Server equipment

Anton Seredny, 2016-03-01 16:08:15

Now one of the sites takes 3 seconds to wait only for the server response. Google recommends no more than 200ms.
The question arose - how is this response time calculated?
Those. response time is the time that has passed since the moment of the request and while the server has processed all php, muscle requests and started to issue content?
If so, then the optimization of queries to the database will help reduce the response time, or is it somewhere with hosting troubles?