On-page SEO and Off-page

On-page SEO includes the on-page factors that tell search engines what your website is about. For example, mentioning your desired keyphrase frequently in your website tells the search engines that it is an important topic on your site. Mentioning your keyphrase in your title tag also strengthens your page's relevancy to that keyphrase. Off-page SEO includes external factors such as backlinks.

on-page SEO refers to SEO done on your physical website. For example, having title tags that contain the keywords that you want to rank for is one of the many good practices when practicing on-page SEO.