Are you talking about SEO? If so on page is things like meta titles, keyword density, source code structure etc.

Off page work would be link building etc.

On-page is one which reflect changes on your website like hyperlink title optimization or alt attribute image optimization reflect change on website.
Where as, off page does not reflect any change on website like bookmark submission, directory submission and many other technique which help you build backlink.
I hope this may help you.

hi
On-page deals in optimization in the coding but Off-Page not involve any coding , link building techniques comes under the Off-Page techniques

Search Engine Optimization (SEO) has become a fine science. Tweaking, changing, and measuring is all part of the ongoing optimization process. SEO truly is a process that requires constant monitoring and attention. In order for a website to perform well, its managers and webmasters must adapt their SEO techniques as the search engine algorithms change.


Use the following "on-page" optimization techniques to improve your website's search engine ranking...

On-Page SEO - On Page Search Engine Optimization Tips

Webmasters have far less control over the "off-page" optimization factors than they do the "on-page" optimization factors. Off-page optimization does, however, influence how a website ranks in search results, so it should not be ignored.

Off-Page Optimization - Optimizing Optimization, Part 2: Off-Page Optimization

On page means works on a site that includes mata tag and content.off page means increase the backlinks of a site.

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SEO means different

the on page means doing the work on your webpage, and offline means doing work related to your web to other web sites

HI.
On page requires programming but off page do not need any programming. On page includes meta tag, meta title, meta description. Off page includes social bookmarking, directory listings, article submission, forum posting.