A large amount of applications now includes tagging mechanisms that have proven efficiency to organize, navigate through, retrieve, and discover online resources. However, despite the valuable research work done to improve these solutions, the literature shows that a further step has to be done in order to better consider the contexts in which tagging actions occur. In this paper, we define a list of elements constituting a tagging context that should be considered in order to better give access to the knowledge shared through users' taggings. We propose an ontological model named ABCT (Activity Based Contextual Tagging) for describing these contexts. ABCT takes benefits from the many research in tagging ontologies and that are synthetized in MUTO (Modular Unified Tagging Ontology). ABCT marries MUTO and PROV (Provenance) concepts to facilitate the description of tags and tagging contexts, essentially through to the notions of Tagging and Activity.