Definition: User-generated-content (USG) is content created and published by the end-users online. USG is comprised of videos, podcasts and posts on discussion groups, blogs, wiki’s and social media sites. USG allows for a wider content provider base and the chance for all users to share their opinions online. Criticism of USG includes credibility and quality issues.
FirstClickSEO Commentary: Social networking sites rule on user generated content. There are ways to add user generated content on most sites and this can leverage you with the search engines.