Average cost-per-click (Avg. CPC) is the amount you've paid for your ad divided by its total clicks. If your ad receives 2 clicks, one costing $0.20 and one costing $0.40, your average CPC for those clicks is $0.30.
Note that Avg. CPC may at times be higher than Max. CPC. For Hotel Ads, this is typically because the Max. CPC is multiplied by the number of nights in the itinerary. For example, if Max. CPC is set at $2, then the most that a click will cost for a 1-night stay is $2. For a 3-night stay, the most that a click will cost is $6. The Avg. CPC will reflect the full price you pay for each click.