Cost per click refers to a pricing structure for ads online where the advertiser is charged whenever someone clicks on the ad. The price of each click depends largely on the amount of competition for a particular ad placement. This term is used almost exclusively with Google Search Ads. The cost for search ads depends on how much the competition is willing to pay for an ad placement.
However, you might see references to CPC in brand awareness campaigns as well. At the end of the day, CPC refers to the cost of a click whether it was a search ad or brand awareness ad. In a Google Search Ad campaign you pay directly for the ads. With a brand awareness campaign you pay for the impressions, and the click is a secondary metric and the cost of the click is derivative.