Social Media consists of social networking and social bookmarking.
A social network is made up of individuals (or organizations) called “nodes,” which are connected by friendship, kinship, common interest, financial exchange, dislike, beliefs, relationships etc. Internet social networks include; Myspace, Facebook, Plaxo, Bebo, LinkedIn and Twitter. Myspace, Plaxo, and Bebo are now populated with age groups 10-21 and 45-60. Facebook and LinkedIn are populated with people 21-35. Demographics of the network should be considered and research is recommended, so that your target market is reached.
The rest of the social media sites are considered social bookmarking sites. Delicious, Digg, Squidoo and Yahoo! Bookmarks are just a few of them. There are more than a hundred social bookmarking sites. At social bookmarking sites users can bookmark frequently visited sites, post blogs, post to social networks and various other things.