SEM (search engine marketing) is the practice of using paid search advertising to capture intent-based traffic from search engine results pages. It runs primarily through Google Ads and Microsoft Ads (Bing), with bidding done at the keyword or audience level and pricing set by auction. It is the paid counterpart to SEO in the broader category of search marketing; in modern usage, "SEM" is typically used to mean paid search specifically, even though the original umbrella definition included both paid and organic.
The terminology genuinely is a mess. Historically, "SEM" referred to all search marketing activity (paid + organic = SEO + paid search). Over the last decade, common industry usage has narrowed SEM to mean paid search only, with...