If an ESXi host was connected to a Distributed Virtual Switch (DVS) and you were not able to properly remove it from the vCenter inventory, which cleans up the VDS as part of the removal, then you will be left with a stale VDS configuration.
Of course, the ideal workflow is to clean this up within vCenter Server but if you some how lost access or the vCenter Server was deleted and you might be wondering how to manually clean this up?