pay per click
pay per click is used in two ways one is to not have to do seo or make your site search engine friendly you just pay and get seen as adds. you can pay little and be seen every so often or bid high prices so that you are always at the top

Most eCommerce sites for large companies take the second approach where they make a search engine friendly site, the pay for seo and they pay for click. the hope is that they can double up on the site, so they can be top of organic search engine optimisation and on the adversts giveing them two chances at the viewer choosing them.