There are plenty of marketing acronyms that markers have to keep track of like SEO, SEM, SMO, CRO. It can be difficult to keep everything straight, especially the difference between SEO and SEM. So, what exactly does SEM mean? Search engine marketing (SEM) is a sort of umbrella term that covers search engine optimization and paid advertisements. SEM is an effective way for businesses to reach new customers, increase revenues and trim acquisition costs.