1. Rest: This is the most straightforward case. If an object has zero acceleration, it means its velocity is not changing. If it was at rest to begin with, it will remain at rest.

2. Constant Velocity: An object moving at a constant speed in a straight line also has zero acceleration. Its velocity isn't changing in magnitude or direction.

3. Uniform Circular Motion: This might seem counterintuitive, but an object moving in a circle at a constant speed also has zero *tangential* acceleration. While the object is constantly changing direction, its speed remains the same. This means the object experiences a centripetal acceleration, which is always directed towards the center of the circle, but the *tangential* acceleration is zero.

So, while the most common understanding might be rest and constant velocity, it's important to remember that uniform circular motion also fits the criteria of zero acceleration (in the tangential direction).