Ontology has been collecting a lot of attention recently. In fact, it has potential for resolving several key problems such as semantic tag design for semantic web, semantic integration, knowledge sharing/reuse, etc. However, it is also true that people have different understanding of ontology. This article is written to contribute to clarification of the understanding of ontology and ontological engineering and to promotion of its utility. Although the discussion is made in the context of Artificial Intelligence in Education domain, I believe the content is pretty general.