What is an example of Deceleration?

That's a word often used to mean "slowing down". An example is what happens

when the brake is applied in a moving car.

But 'deceleration' is a very unofficial, unscientific word. If the forward speed

is decreasing, then a much more useful concept is "negative acceleration".

When the body starts moving with a slower speed than the initial speed and it slows down continuously, the this is called deceleration. Examples of deceleration -

When a ball is thrown upwards, its speed goes on decreasing as its height increases.

When a car applies brakes.