acceleration

In everyday language, the term acceleration is used to describe something that is speeding up, while deceleration is used to describe something that is slowing down. In physics, the word deceleration is not used at all. Instead, physicists talk about positive and negative acceleration.

To understand this better, think about an object that is slowing down continuously until it stops, and then it starts to speed up and go backwards. The object is involved in one continuous process, so it does not make sense to use two different and opposite terms (acceleration and deceleration) to describe the same process.

Acceleration is simply a vector quantity that involves a magnitude and a direction. Write a few short scenarios involving motion, in which you describe what is happening in everyday terms, including deceleration.