The term formal itself was coined by Edmund Husserl in the second edition of his Logical Investigations (1900-01), where it refers to an ontological counterpart of formal logic. Formal ontology for Husserl embraces an axiomatized mereology and a theory of dependence relations, for example between the qualities of an object and the object itself. Formal; signifies not the use of a formal-logical language, but rather: non-material, or in other words domain-independent (of universal application).”
Jonathon Lowe in The Oxford Companion to Philosophy described ontology as “the set of things whose existence is acknowledged by a particular theory or system of thought.”
material, physical and concrete
Objects consisting of matter (or energy). Not abstract. Three terms used interchangeably.
A model of an ontology. An ontology can have multiple models.
The fundamental structures of the ontology. Typically includes the major choices of ontological commitment. Can function as a blueprint for developing an ontology.