Social Bookmarking
What it is:
Social bookmarking allows you to use tags for more than just remembering. Through social bookmarking site, you can share your own bookmarks/tags, as well as explore those of other users.
Tagging
What it is:
A tag is a piece of metadata (e.g., a keyword or term) assigned to a piece of digital information (such as an internet bookmark, image, or computer file). Tagging is classifying content for other uses later, including "re-finding" it and sharing it. Tagging is closely related to social bookmarking.