Folksonomy refers to a system of classification created by users to tag and organize online content. It emerged in the early 2000s as sites like Delicious allowed users to tag websites and resources with keywords. The term was coined by Thomas Vander Wal to describe this social or "folk" taxonomy. While tagging provides advantages like easier browsing and self-expression, it also presents disadvantages like potential miscommunication, lack of control over one's tags, and privacy issues.