Frame rate
How many pictures a moving image shows each second, such as 30 or 60.
See it in Cellular automata. Press Play, then change Generations / sec to speed the grid up or slow it down.
In plain words
Moving pictures are still pictures shown quickly one after another. Frame rate is how many of them appear each second. Film often uses 24, most phones and screens show 60, and some show 120. A higher frame rate makes motion look smoother. If a tool cannot draw a frame in time, the rate drops and motion stutters.