there and back again
Ping (latency) is the time it takes for data to transmit from your device to an internet server and back to your device again.An easy way to think about ping is the reaction time of your internet. If you have a faster ping, you can expect almost no delay when inputting commands.
If you have a very slow ping however, you will likely notice a significant delay (or input lag.) Having a good ping is an important part of your broadband package and is imperative when online gaming, as this will likely mean the difference between winning and losing in competitive sessions.
(This is particularly noticeable in games like League of Legends or Call of Duty where faster reactions are needed.)