Lag is a term indicating the latency (i.e. tendency for delay) of a particular Internet connection.
More lag means a longer time is required for a player's moves to be communicated to the game server, which can make it seem as though the player is moving somewhat more slowly. The difference is not usually very important for standard chess games, but can have a big effect on blitz and bullet games. Therefore, the game timer takes relative amounts of lag into consideration when determining how much time a player actually took to move.
Next to each player's name you may see a colored lag indicator (a small colored bar) which shows how good or bad that player's connection is: Excellent Connection (very low lag), Good Connection (low lag), OK Connection (some lag), Poor Connection (high lag).
The maximum amount of lag the system will compensate is two seconds.
keywords: lag, latency, live chess, timer, time, clock