3D geoscience models lack transparency about the interpretation process and the assumption to model and represent geological entities, limiting explainability, reproducibility, and automation. To address this, we present POKIMON (Processes, Observations, Knowledge, Information, and Modelling ONtology), an ontology that formalizes the expert knowledge, interpretative aspects, and geological entities descriptions underlying 3D geomodelling, enhancing understanding, transparency, and knowledge-driven automation.