PPC is short of Pay-Per-Click. It is a form of paid advertising on the Internet. It is a type of advertising when you only pay when someone clicks on your ad. You don’t pay for someone seeing your add which is called an impression.
The beauty of PPC is that you only pay when someone shows intent that they are interested in your product or service.
For more information, here is a great article. https://blog.hubspot.com/marketing/tabid/6307/bid/1514/paid-search-vs-organic-search.aspx
