What is meant by uniform acceleration

Uniform acceleration basically means acceleration that is constant, the same speed or velocity the whole time. Nothing more to add really.

When an object undergoes uniform acceleration, its velocity changes by the same amount per unit of time.

For example, a person jumping off a cliff into a pool of water below undergoes a uniform acceleration of approximately 9.81m/s². This means that, for every second that passes, the person's downward velocity increases by 9.81m/s