physicalEntity

Definition: An entity with a physical structure. A pool of entities, not a specific molecular instance of an entity in a cell. Comment: This class serves as the super-class for all physical entities, although its current set of subclasses is limited to molecules. As a highly abstract class in the ontology, instances of the physicalEntity class should never be created. Instead, more specific classes should be used. Synonyms: part, interactor, object Naming rationale: It's difficult to find a name that encompasses all of the subclasses of this class without being too general. E.g. PSI-MI uses 'interactor', BIND uses 'object', BioCyc uses 'chemicals'. physicalEntity seems to be a good name for this specialization of entity. Examples: protein, small molecule, RNA

Source:http://www.biopax.org/release/biopax-level2.owl#physicalEntity