Slow in and slow out
Refers to the timing of an object or figure at the beginning or end of a sequence. ‘Slow In’- an action decelerates into a key frame meaning that the object will move slower. ‘Slow Out’- an action accelerates out of a key frame meaning that the object moves faster. Most actions will involve both a slow in and slow out to make the movement of the object look more realistic.
A bouncing ball is the most basic example to represent this principle as it uses both actions, this is called 'Variable Action' it shows acceleration and deceleration within a sequence. A contemporary example of this would be the Pixar Logo animation as both 'Slow In' and 'Slow Out' is used to control the speed of the bounce within the lamp.