For a moving body at any instant of time

Suppose throwing a ball vertically up. At the highest point. It is at momentary rest but acceleration g still acts downwards.

If the body is slowing, the acceleration is negative which means the retardation is positive.

If the body is slowing, the displacement can be increasing( positive velocity).

If displacement, velocity and acceleration at that instant are known, we can find the displacement at any given time in future. 

using $\mathrm{x}={\mathrm{x}}_0+\mathrm{ut}+\frac{1}{2}{\mathrm{at}}^2$