For semi-technical detail go here: http://en.wikipedia.org/wiki/Ping
So "ping" time is the round-trip time between your computer and the far end device. As to trading - In my opinion if your trading is intra-day and based on immediately reacting to tick data it might have an effect on your trading. This also depends on what you trade. The times involved for most of us retail traders are typically in the 40 to 200 millisecond range. So if you are competing with a professional trader who has his trading automated and running on a computer right next to the exchange your 40 milliseconds will never beat their 2 milliseconds or less.
The best use for the ping test is to ensure that your system is connected and running reliably over the internet. The PingPlotter program allows you to capture and plot the ping time to each node along the internet path.. Running it when you are having difficultly can help you in convincing your internet service provider that there is a problem.
Jack
What does that mean?