complex

Definition: A physical entity whose structure is comprised of other physical entities bound to each other non-covalently, at least one of which is a macromolecule (e.g. protein, DNA, or RNA). Complexes must be stable enough to function as a biological unit; in general, the temporary association of an enzyme with its substrate(s) should not be considered or represented as a complex. A complex is the physical product of an interaction (complexAssembly) and is not itself considered an interaction. Comment: In general, complexes should not be defined recursively so that smaller complexes exist within larger complexes, i.e. a complex should not be a COMPONENT of another complex (see comments on the COMPONENT property). The boundaries on the size of complexes described by this class are not defined here, although elements of the cell as large and dynamic as, e.g., a mitochondrion would typically not be described using this class (later versions of this ontology may include a cellularComponent class to represent these). The strength of binding and the topology of the components cannot be described currently, but may be included in future versions of the ontology, depending on community need. Examples: Ribosome, RNA polymerase II. Other examples of this class include complexes of multiple protein monomers and complexes of proteins and small molecules.

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