On-page SEO is the practice of optimizing a website for Google search with the goal of earning higher web traffic levels and improving the visibility of the site. The main focus of on-page SEO is to tweak titles, metatags, keyword density, site structure and content quality.
Off-page SEO is the practice of building backlinks to a website with the goal of earning higher web traffic levels and improving the visibility of the site. The main focus of off-page SEO is to find other websites in your niche that are willing to link back to your site. This can be done by guest blogging, forum posting, directory submission, social bookmarking and more.