This type of thing is worth a whole nother category of its own (see the disambiguation tag).
Folksonomies and collabularies (online ontologies)
Says Paul Anderson (2007) in a recent report for JISC Techwatch:
One outcome from the practice of tagging has been the rise of the ‘folksonomy’. Unfortunately, the term has not been used consistently and there is confusion about its application. More will be said about this in the section on network effects, but for now it is sufficient to note that there is a distinction between a folksonomy (a collection of tags created by an individual for their own personal use) and a collabulary (a collective vocabulary).
Constructionivism and constructivism
Constructionism … shares constructivism’s connotation of learning as “building knowledge structures” irrespective of the circumstances of the learning. It then adds the idea that this happens especially felicitously in a context where the learner is consciously engaged in constructing a public entity, whether it’s a sand castle on the beach or a theory of the universe.” (Papert, 1991, p1)
Anderson, P (2007). What is Web 2.0? Ideas, technologies and implications for education. A JISC TechWatch Report, February 2007. Available from: http://www.jisc.ac.uk/media/documents/techwatch/tsw0701.pdf
Papert, S. (1991) Situating Constructionism. In Harel, I. and Papert, S. (Eds.), Constructionism. Norwood, NJ: Ablex