Any action you do outside of your website to improve the authority and credibility of your web pages and, as a result, their likelihood of ranking well in organic search, is known as off-page SEO. On the other hand, link building, which is a component of off-page SEO, is obtaining links from other websites that point back to yours in order to let Google know that your website is a reliable source.
Contrary to popular belief, link development is not the only aspect of off-page SEO. Without a question, link building is a crucial component of off-page SEO since Google considers each credible backlink to your website as a vote of confidence.
However, guest posting, press releases, requesting brand mentions (your brand name mentioned on another website without a backlink), submitting your site to directories, etc., are all a part of off-page SEO.