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1. A division within a system of classification.
2. Any of several fundamental and distinct classes to which entities or concepts belong. Reference: Merriam-Webster Collegiate Dictionary 2004 v.3.1 electronic edition.
3. [BFO2.0] A formal (which is to say, domain-neutral) universal, such as entity, continuant, or occurrent. [ Arp et al., 2015 ]
4. A property that is rigid but does not carry a specific identity criteria. [ Guarino, 1999 ]