What’s social media? What’s Web 2.0?

This week, I read an article, named “Social Media and Instructional Design” on another course textbook, wrote by Dr. Dennen. This article describes social media’s definition “Social media are Internet-based tools that allow users to build networks through which they may then communicate and share information with each other.” I understand social media are tools to underpin people communicate/interaction/cooperation online. When social media are used as instructional tools, they possess benefits for learners such as they can broaden learners’ communication/engagement/discussion from in-class to out-class, extending the boundaries of the classroom. Additionally, social media may be used to expand feedback’s scope from a wider audience, not only classmates, instructors but also experts of specific fields. Furthermore, learners may search for more relevant materials via online networks.  
In addition to these advantages, there also are some challenges of using social media as instructional tools. First, the driving force behind social media adoption in education should be learning objectives and context, not other external pressures, such as many learning organizations is enthusiastic to social media in their lessons. Second, social media technologies distract learners, especially young learners without self- controlled componence.

Web 2.0 may allow users to interact and collaborate in a virtual community. It is obvious that Web 2.0 is a platform with tools such as social media, social networking sites, video sharing sites, Web applications(”app”), etc. to underpin people communication and cooperation.
I think the relationship between Web 2.0 and social media is interdependent. I agree with Dr. Dennen that it is difficult to make sense who is the first one to come out like chick and egg.