Lag is a word that means to fail in keeping pace or to fall behind. This term is used a lot by people who are talking about video games that have a delay between when a player presses a button on a controller and something happening in the game. This happens more often during online gaming when the access point a player is using is far away or when other players are using slower connections, such as dial-up. The slowing down of a website when more people get onto that website can also be called lag.