What is ping, and why do online games lag?

Ping is the round-trip delay between your game and the server, measured in milliseconds. It is not the same as bandwidth (how much data fits per second) or packet loss (messages that never arrive).

Because the server is the referee and every player sees a slightly old version of the match, you can get shot behind a corner. Drag a player in the simulator to see delay and rubber-banding for yourself.