Search Engine Marketing (SEM) refers to techniques used to drive traffic to a website from search engines results. When a user conducts an online search, the search engine (Google, Bing, Baidu) responds by compiling a series of free and paid listings. These are served on a “search engine results page” (SERP).

The search engine displays the free listings it collected based on relevant on-page SEO (keyword, content, information architecture, internal linking, social media integration, etc.) and off-page SEO (link building). It also displays related paid results, like search ads, product listing or shopping ads, display and banner ads, mobile ads, social media ads, retargeting and remarketing, in-app ads, etc. Marketers use a mix of free, organic listings, and paid ads to gain visibility and entice users to visit their site.