What is Web 2.0 in SEO and what is its role in SEO

WEB 2.0 - SEO Techniques, SEO Tips

Web 2.0 is a new version of web development & design so doing SEO of web 2.0 based sites is known as web 2.0 in SEO. 
Web 2.0 submission includes the blog posting. In web 2.0 submission where SEO marketers create their blog in different web 2.0 sites. It's completely one of trendy and easy option of link building. It's really a good way for the brand promotion. In this you can share link with your fellow bloggers to increase traffic on your site.

It also include creating link bait, socializing. It generates traffic on your site.

The main traffic source is Facebook, twitter, Google Maps, Google Images and Product Searches.
Its follows bottom up approach. Learn the difference between SEO 1.0 & SEO 2.0