tagging

Tagging is the act of assigning keyword-like labels, or tags, to digital objects such as documents, images, videos, or data entries. Tags are typically user-generated and informal, providing flexible, ad hoc categorization that complements formal metadata and controlled vocabularies.

Tagging arose with social bookmarking and other collaborative platforms in the early 2000s. Pioneering tagging systems such as Del.icio.us popularized user-generated tagging. The concept of a folksonomy—a bottom-up classification created by users—contrasts with top-down, curated taxonomies.

How tagging works: users attach tags to items; tags may reflect topics, attributes, or contextual meanings. Tags often appear in tag clouds or filters, and they support search, navigation, and discovery. Systems may allow synonyms, tag merging, and occasional hierarchical relationships.

Applications span social media hashtags for grouping posts, photo and video libraries that enable retrieval by subject, code repositories that use tags for topics or releases, and digital libraries that supplement subject headings with user-added tags.

Advantages include flexible, scalable organization and user-driven discovery. Criticisms focus on inconsistency, ambiguity, and language variation; tag synonyms, duplicates, and spam can reduce reliability and interoperability across platforms.

Related concepts include taxonomy, controlled vocabulary, metadata, and ontologies. Tagging remains a foundational technique in information organization, with ongoing discussions about balancing user autonomy with standardization to improve search and interoperability.