Google AdSense is a program run by
Google
that allows publishers in the Google Network of content sites to serve
automatic text, image, video, or interactive media advertisements, that
are targeted to site content and audience. These advertisements are
administered, sorted, and maintained by Google, and they can generate
revenue on either a
per-click or
per-impression basis. Google
beta-tested a
cost-per-action service, but discontinued it in October 2008 in favor of a
DoubleClick offering (also owned by Google).
In Q1 2014, Google earned US $3.4 billion ($13.6 billion annualized), or 22% of total revenue, through Google AdSense.
My youtube video on how to set it up on your youtube page