A keyframe that inherits its value from the previous keyframe
Imagine a scenario with 3 keyframes where an object holds position for a second (1-2) then moves to a new position (2-3). To adjust the object hold position, you must edit keyframes 1 and 2. If you forget to update keyframe 2 you no longer have a hold. With this type of inheritance keyframe, you'd only have to worry about adjust keyframe 1, and keyframe 2 would automatically follow along.