1. Auction system: A mechanism where advertisers compete for keywords and bid prices per click (CPC) or per thousand impressions (CPM).
2. Ad targeting: The use of sophisticated algorithms to target ads based on demographics, user behavior, and search history.
3. Extensive partner network: the Google Display Network (GDN) includes many websites on which ads can be displayed, increasing the reach of advertisers.
4. Mobile advertising: The ability to display ads on mobile devices, responding to the increase in mobile internet usage.