While SEM and PPC are often used interchangeably, there is a difference between the two.  SEM encompasses both organic traffic (or unpaid) as well as paid advertising activity that intends to improve how easy it is for people to find your website through search engines (Search Engine Optimization) or other channels such as video ads or picture ads (Content Marketing). On the other hand, Pay-Per-Click only refers specifically to online advertisements that work with search engine results pages and marketplaces like YouTube/Instagram/Facebook, where you pay every time someone clicks on your ad.