Web 2.0 submission is an SEO technique. In which you share your content to sites that allow you to make an account and submit content. The sites are such as hongkiat, hubpages, squidoo, skillonpage, etc. Getting backlinks from those sites are more valuable for your site's rank on Google. Facebook, Twitter, and Linkedin are also web 2.0, however, having your links on these sites will not have great impact towards your site's ranking.