Ping is "Packet Inter-Networking Groper", the time it takes for a network packet to leave your computer, go to another one, and return.
Lower = better. Can also be a source of gloating in network games. Typically measured in milliseconds.
So..if you play on a server with 120 in ping and the rest of the players have 20 in ping. All the other players will be 0.1 sec ahead. So if you want to own on a server with that high ping; shoot infront of running players and always spray :lol:
...or just play on a server closer to you. :)