on-page and off-page forum

What is Onpage and Offpage optimization?
I have seen many web sites who really don't have clarity about what is On page what is Off page optimization? How it make sense to improve the web site traffic building.
Are you interested to launch a website first you need to understand the link building strategy. Otherwise, it is useless website. No one remembers website url, even though you are A one class memory you may get few traffic only. To maximize you traffic
I did little googling found the following links interesting 

http://forums.site-reference.com/topic/11539/On-page-and-Off-Page-Optimization-techniques/

http://forums.site-reference.com/topic/12795/Backlinks/

http://www.seo24by7.com/social-news.php

http://www.seomoz.org/blog/the-wonderful-world-of-seo-metatags