The “Overshoot” in animation is like when a character moves a little bit beyond their destination before returning to their correct position. It’s as if they have a “bounce” or an “inertia” that makes them move a little beyond the stopping point before coming to a complete stop. This makes the animation look more natural and organic, as if it were a real movement.
“Ease in Out” in animation is simply adding a gradual acceleration at the beginning of a movement and a gradual deceleration at the end of it, to make it look more natural and organic, as if it follows the laws of physics. It is a technique used to make movements in animation look more realistic and fluid.