ping/latency is the time it takes for a signal from your comp to reach the server and come all the way back.
there is three things that i can think of that affect this.
bandwith: you might have a really fast bandwidth but if some where down the route you use a line with a low bandwidth up goes the ping.
how many routers in the way(every time it hits a network junction this adds time to the route)
Distance: how much wire does the signal have to go down before it hits the server.