When you specify values and keys for a controller, you are defining animation over a range of time. You choose Out-of-Range Types to determine how the animation continues outside a specified range. Out-of-Range choices include holding a constant value, and various ways of repeating the animated range.
The easiest way to work with Out-of-Range Types is in the Track View Function Curve mode.
You use the Parameter Out-of-Range dialog to project the pattern of the key dots in the selected track. These patterns are applied to the animation outside the range of all keys in the track. This is why they're called out-of-range types.
By default, tracks use a constant out-of-range type. This means that the track values before and after the range of keys remain constant. For example, in a 100-frame animation with keys up to frame 20, the X, Y, and Z values after frame 20 remain the same for the rest of the animation. The objects in this example do not move from frame 20 to frame 100.
Applying the Cycle out-of-range type will make the key pattern in frames 0–20 repeat cyclically for the remaining 80 frames.