1. SEM: Stands for Search Engine Marketing, and as the name implies it involves marketing services or products via search engines. SEM is divided into two main pillars: SEO and PPC. SEO stands for Search Engine Optimization, and it is the practice of optimizing websites to make their pages appear in the organic search results. PPC stands for Pay-Per-Click, and it is the practice of purchasing clicks from search engines. The clicks come from sponsored listings in the search results.