On-page and Off-page are both part of SEO techniques. On page techniques increase the visibility of a webpage and make it search engine friendly. it includes URL optimization, H1 tag, image optimization, w3 validation, keyword density, content optimization.
And, Off-page techniques generates quality and quantity of backlinks which increase search engine results. It includes forum posting, social bookmarking, directory submission, article marketing, classifieds posting, blog posting.

On page is about making web pages optimized so that search engines found them easily and know what niche they occupies ...
Off pages : off page techniques are in order to build back-links for website