The power rating of any electrical equipment is the highest power input allowed to flow through particular equipment. In order to guarantee safety and performance, manufacturers set power rating limits as a guideline. VAC stands for Volts Alternating Current.
The limits are provided as a range and the range varies across the world. For example, in parts of Japan, the voltage can be 100V AC, and the US/North America where its 120V AC. However, in the UK and most of the rest of the world, it is 230-240V AC.