Cost- Per- Click (CPC) can be explained as the cost paid by advertisers for every click through on their advertisement. Many search engines also run paid advertising campaigns where advertisers pay to have their advert pop up on relevant searches. They then pay the webmaster for every click that their advert gets. This is also sometimes referred to as Pay- Per- Click (PPC) advertising.

If you would like to define each term then PPC advertising would be referring to the advertisement based on click-throughs and CPC would be referring to the actual price paid for each click.