The position of the Actor is interpolated linearly between the first keyframe and the following keyframe.
For example, if the Actor has movement timelines in frames 1-1 and 2-10 and it is at (0,0,0) in frame 1 and at (10,10,0) in frame 10 then it will be at (5,5,0) in frame 5. Put simply, in half the time it will move half the distance.
A linear or straight line track is visible in the Working-Volume when the Spline Tween Mode is enabled.
Note: The default Movement Timeline setting is Tween.