flag of conveniencenoun [ C usually singular ]
uk/ˌflæɡ əv kənˈviː.ni.əns/us/ˌflæɡ əv kənˈviː.ni.əns/UKIf a ship sails under a flag of convenience, it means it is operated or taxed under the laws of a country different from its home country in order to save money:
They always register their ships under a flag of convenience.