Qualities in reality. (from http://ontology.buffalo.edu/bfo/Terminology_for_Ontologies.pdf)
An abstract or general idea inferred or derived from specific instances, representing a set of those instances.
The conceputal representation of anything that is a property (a thing that is inherent in an entity, like eye color) or an attribute (a thing that has been assigned, or attributed, to an entity, like name or identification number).
Universal (natural) sets of objects, processes, qualities, states, etc. in reality (for example on the side of the patient); (from http://ontology.buffalo.edu/bfo/Terminology_for_Ontologies.pdf)
Concepts represent universals in the world.
Things in the real world can be represented by concepts. This is a link from the concepts and the things those concepts represent. Concepts represent things.
A concept representing the relationship between two independent entities.
A conceptual type can have qualities that describe it.
Things in the real world can be represented by concepts. This is a link between the concepts and the things those concepts represent. Things, including sets of things, are represented by concepts.
Relationships in reality. (from http://ontology.buffalo.edu/bfo/Terminology_for_Ontologies.pdf)
Entities that describe the objects, processes, qualities, states, etc. in reality (for example on the side of the patient); (from http://ontology.buffalo.edu/bfo/Terminology_for_Ontologies.pdf)