Wiktionary
social bookmarking
n. a way for Internet users to share bookmarks or shortcuts to online resources
Wikipedia
Social bookmarking
Social bookmarking is a centralized online service which allows users to add, annotate, edit, and share bookmarks of web documents. Many online bookmark management services have launched since 1996; Delicious, founded in 2003, popularized the terms "social bookmarking" and " tagging". Tagging is a significant feature of social bookmarking systems, allowing users to organize their bookmarks and develop shared vocabularies known as folksonomies.