CPC is a an acronym for Cost Per Click, which is the price that an advertiser would pay when an display advert is clicked. In the Toolbox, this value refers to the click price for Google Ads.
The value shown should be considered an average value. In reality, Google optimises for sales, which means the product of the click rate and the click price for each ad. Because of that, the paid price can vary a lot between advertisers.
In addition, the CPC is continually varied through an auction system. It can vary due to time-of-day, season and many other factors. The average value displayed in the toolbox should be considered with these factors in mind.