On-page SEO refers to SEO factors and techniques focused on optimizing the aspects of your website that are under your control. Off-page SEO refers to SEO factors and strategies focused on promoting your site or brand on the web. Off-page SEO refers to all SEO tactics that don't involve updating or publishing content to your website. In simplest terms, on-page SEO encompasses all the actions you take on your website to affect your search engine rankings.
Off-page, on the other hand, happens outside your website.