When a body has zero acceleration, it means that its velocity is not changing. The body could be at rest (zero velocity) or moving at a constant velocity. In either case, zero acceleration implies that there is no net force acting on the body, or that any forces acting on the body are balanced.
On the other hand, when a body has negative acceleration (also known as deceleration or retardation), it means that its velocity is decreasing. The body is slowing down in the direction of its motion. Negative acceleration can occur when a force opposes the motion of the body, causing it to decelerate.
It's important to note that while negative acceleration refers to a decrease in velocity, the body can still be moving in the positive direction. The negative sign indicates the change in velocity, not the direction of motion itself.
In summary, zero acceleration indicates that there is no change in velocity, while negative acceleration implies that the body is slowing down in the direction of its motion.