* Velocity at the top: When a rock reaches the highest point of its trajectory, its upward velocity has been completely reduced to zero. It's momentarily paused before gravity pulls it back down.

* Acceleration at the top: Even though the velocity is zero, the rock is still under the influence of gravity. Gravity constantly pulls objects downwards, resulting in a constant downward acceleration.

In summary: At the top of its path, the rock has zero velocity (it's not moving up or down at that instant) but still has a constant downward acceleration due to gravity.