I agree that most tagging is collective - but I have talked to people thinking about tagging within an enterprise and scenarios where teams form social contracts with each other and agree on common tagging strategies - I would define that as collaborative tagging vs. collective tagging. There is an intersect, or perhaps its a subset, between collective tagging (individuals acting alone that coincidently apply similar tags) and collaborative tagging (groups that agree on a tag vocabulary and apply those tags related to artifacts within a collaborative activity (e.g., a project). Collaboration should not so narrowly be defined and applied only to a single artifact within joint work (e.g., a wiki page). Collaboration has multiple levels and can involve coordination across co-dependent artifacts with varying degrees of symmetric "joint work" on group and individual artifacts within that project.
Collaboration and collective efforts are often confused by those not familiar with both terms, but they are not similar and they are two distinctly different efforts. Collaboration is people working together (often with a common goal) to build one thing (think wiki page with one understanding). Collective efforts are the aggregation of people's individual efforts, sometimes in the same service, but do not have common goal or common effort (del.icio.us page for a URL is the collective understanding of individuals tagging of that page for their own use.