Digital marketing refers to using digital channels like websites, search engines, social media, and email to promote products and services. It includes tactics like SEO, PPC, social media marketing, and content marketing to engage target audiences online and drive leads, sales, and revenue. SEO involves optimizing websites to increase search engine rankings organically. SMM is promoting products on social media platforms to build brand awareness and engagement. SEM uses paid search advertising like PPC to promote websites and increase visibility in search results.