Frame rate is how many images a camera captures per second. Higher rates show motion more smoothly and help read a moving plate or a running person; lower rates reduce storage and bandwidth. A frame rate above what the scene needs buys nothing and costs recording space.
Frame rate is usually set once and forgotten. It is also one of the settings that most directly decides whether a fast event is legible in the recording.
Frames and motion
At a low rate, a person walking through a doorway may appear in one frame or none. Higher rates capture more positions, which helps with movement but multiplies the data. Scenes with vehicles, gates or fast foot traffic need more frames than a quiet corridor. Record the rate you chose, because it explains later why a clip looks the way it does.
Sizing frame rate with bit rate
Raising the frame rate at a fixed bit rate gives each frame fewer bits, so the picture softens as smoothness improves. Decide what matters for the scene, then set the bit rate to support that choice. Frame rate is not a free setting.