PPC Advertising
Google AdSense is the most popular option under this category, but there are also others. Basically you need to sign up with the network and paste some code snippets on your website. The network will then serve contextual ads (either text or images) relevant to your website, and you will earn a certain amount of money for every click.
The profitability of PPC advertising depends on the general traffic levels of the website and, most importantly, on the click-through rate (CTR)
