any North American plant of the genus Iris, especially I. versicolor: the state flower of Tennessee.
Origin of blue flag
An Americanism dating back to 1775–85
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for blue flags
an award given to a seaside resort that meets EU standards of cleanliness of beaches and purity of water in bathing areas
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012