Timing function (also known as easing) are used in transition to calculate the speed and smooth of the animation between state.
They specify the rate of change of a parameter over time.
Objects in real life don’t just start and stop instantly, and almost never move at a constant speed. Drop something on the floor, and it will first accelerate downwards, and then bounce back up after hitting the floor.
Timing Curves describe the pace with which a transform changes between each keyframe. Each timing curve is modeled as a cubic bezier curve from point [0, 0] to [1, 1], where the X value is the progression in time from the origin keyframe to the destination keyframe, and the Y value describes the amount of change in the value at a given time:
<MATH> origValue + (destValue - origValue) * Y </MATH>
They are generally: