Lag may refer to any of the following:
1. In general, lag is the time difference a performed task and its result. For example, the fraction-of-a-second pause between the time a keyboard key is pressed and the time it takes to appear on the screen.
2. In gaming, lag refers to any noticeable slow response in an online game due to high latency or a poor connection. For example, on a slow Internet connection your character or the environment they're in may stutter.