Off-page SEO refers to activities done outside of one's own website to improve search engine rankings, such as social media engagement, social bookmarking, forum posting, blog commenting, article submission, question & answer participation, video sharing, image sharing, and document sharing. These off-page techniques help make a website more popular on the internet and improve its search engine rankings by increasing backlinks from other relevant sites. The document provides examples of popular social media platforms, bookmarking sites, forums, article directories, Q&A sites, video sharing sites, image sharing sites, and document sharing sites for off-page SEO activities.