Final answer:
When a quantity is expressed as '4cm/sec', it is describing the speed or velocity of the quantity at a rate of 4 centimeters per second.
Step-by-step explanation:
The expression '4cm/sec' is describing the speed or velocity of a quantity. In this case, it represents a rate of change of distance over time. It means that the quantity is moving at a speed of 4 centimeters per second.