Ping latency measures how long it takes to receive a result for a request from the outside exchange. Things are working normally is there’s a low number between 10ms and 37ms (milliseconds). A ping latency above 37ms can be an early warning sign that there's a problem with your broadband speed.
Packet loss is where only parts of the request to the outside exchange are coming through. This means that something is wrong and additional testing is needed.
Ping latency and packet loss have many causes including faulty equipment, wireless interference, and noise on your line. Both ping latency and packet loss can affect your broadband speed. How to use BT broadband speed tests.