Oxford Dictionaries: “Folksonomy, a portmanteau word for ‘folk taxonomy’, is a term for collaborative tagging: the production of user-created ‘tags’ on social media that help readers to find and sort content. In other words, hashtags: #ThrowbackThursday, #DogLife, #MeToo. Because ordinary people create folksonomy tags, folksonomies include categories devised by small communities, subcultures, or even individuals, not merely those by accepted taxonomic systems like the Dewey Decimal System. The term first arose in the wake of Web 2.0 – the Web’s transition, in the early 2000s, from a read-only platform to a read-write platform that allows users to comment on and collaboratively tag what they read. Rather unusually, we know the exact date it was coined: 24 July, 2004. The information architect Thomas Vander Wal came up with it in response to a query over what to call this kind of informal social classification.

Perhaps the most visible folksonomies are those on social-media platforms like Facebook, Twitter, Tumblr, Flickr, and Instagram. Often, people create tags on these platforms in order to gather under a single tag content that many different users have created, making it easier to find posts related to that tag. (If I’m interested in dogs, I might look at content gathered under the tag #DogLife.) Because tags reflect the interests of people who create them, researchers have pursued ways to use tags to build more comprehensive profiles of users, with an eye to surveillance or to selling them relevant ads…”