"Ping" is basically the time it takes for a "packet" another computer or server\website.
Ping and Lag
Have you ever noticed that it was taking time for a person to die even though you killed them 5 second before? Have you also noticed that on the bottom a meter read something like "800 MS" or even "2000 MS". Well that is because it is taking 800 milliseconds (MS = Milliseconds) for a "packet" from your computer to reach Pawn Tactic's server. In this case, the packet contains information about what you did on Pawn Tactics. However, if it takes a while (a "while" can be as short as a split second) for that packet to reach Pawn Tactic's servers, it can cause lag.
How to fix
There is only one reason why high ping times happen and that is a slow internet connection. That means that either your computer or Pawn Tactic's servers are connecting to the Internet on slow connections. To check if it is your connection that is slow, open up a website. If it loads very slowly (or doesn't load at all), then you likely have a problem with your internet connection. Otherwise, just wait for Pawn Tactic's servers to be diagnosed.
See also: FPS