Lag is a slow response from a computer. It can be used to describe any computer that is responding slower than expected. However, the term is most commonly used in online gaming.
Video game lag is generally caused by one of two factors – 1) a slow computer or 2) a slow Internet connection. If you are playing an online multiplayer game and your computer cannot process the incoming data in real-time, it may slow the game down for everyone. If your Internet connection is slow or inconsistent (which is common with a shared wireless connection), your system may not send and receive enough data to keep up with other players. This lag may produce choppy frame rates and cause a delay between your input and what happens on the screen.
In an ideal world, all online gamers would have fast computers and fast Internet connections. The reality, however, is that players have a variety of computer systems and significantly different Internet connection speeds. Therefore, video game developers must account for lag in multiplayer games. The preferred method is to make sure lag only affects the individual with the slow computer or Internet connection. This prevents players with high-quality gaming setups from being negatively affected by users with slow systems.
In some cases, a player with a high amount of lag will be booted from a multiplayer game. For example, in StarCraft 2, if a player's system is not responding, a message will appear on the player's screen that says, "Waiting for Server." Other players in the game will see a message that says "Waiting for player: [player name]." If the lag is too high, the player will eventually be booted from the game.
NOTE: "Lag" can also be used as a verb. For example, a player that is "lagging" may be slowing down the game.
Updated: September 26, 2013