The term folksonomy, neologism born from the union of taxonomy (taxonomy) and folk people), is used to indicate a spontaneous and collaborative classification created by users who, by assigning tags, classify images, videos, links, texts, etc. 
This typical "labelling" system of web 2.0 was generally identified as a form of classification, but you must investigate more in depth to understand whether it is actually a form of classification or rather of a system of indexing resources.