Historically in Simbad it was any component of any double system listed in the CCDM or in the WDS catalogues, whatever the separation between the two components, and whatever the physical background. Many components were just "optical" without any physical link. This object type is going to disappear in Simbad as it brings more confusion than useful information. When there is a physical link between the components (including a blend), it is replaced by the hierarchy links between the system and the components.

-- CecileLoup - 2014-02-20