When you will say a body is in
uniform accleration
non uniform accleration
Uniform Acceleration means that the Acceleration remains constant. Suppose a car is traveling at speed of 10m/s^2, it will continue to accelerate at this rate only. For the first second the speed is 10m/s for the second one it's 20m/s and it continues.
Non-Uniform Acceleration means that the Acceleration is not constant. Suppose two cars are racing, in this case, we will look at only one car, if the first one accelerates at the beginning and then decelerates, and then when that car driver sees that the second car is ahead he accelerates again to win. In this case, the driver accelerates and decelerates which means that the speed is variable here.
In the first case, we saw that the speed is constantly increasing while in the second case the speed is variable i.e either increasing or decreasing.
We can distinguish between the two in the following way :
(i) If a body is in uniform acceleration then equal changes in velocity will take place in equal intervals of time,however small these intervals may be.
(ii) If a body is in non-uniform acceleration then unequal changes in velocity might take place in equal intervals of time, however small these intervals may be.