There are two main activities in Seo on page seo and off page seo.In seo people do off page activiy for generate backlinks for their website.There are many off page activites in off page seo
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Offpage seo is a part search engine optimization which is used to improve our website backlinks. It includes some techniques like directory submission, blog comments, social bookmarking, forum posting etc.
I can say that Off-page is one part of SEO, includes bookmarking, forums, directory, pdf, article, press, video. These are helpful for making your site visible to the audience or users in the search engine results page