lag:
Lag is a common word meaning to fail to keep up or to fall behind. In real-time applications, the term is used when the application cannot keep up with performance demand or user input. In other words, it refers to when the application is not keeping up with it's "real-time" concept, due to problems related to poor rate of cycles-per-second, a (possibly cumulative) lateness of response to user input, or other problems.