The Cat's Meow was a term first used in the 1920's during the Flapper era.  The term was used to mean "a highly admired person or thing".  Flappers, were young women of that era who showed off their knees (outrageous!) and would dance until morning.   Their exposed knees coined the phrase "The Bee's Knee's".  These young woman's attire or themselves even may be known as "The Cat's Meow".  The Flappers were the first generation of the new independent women.