Mab, Queen, in fifteenth and sixteenth century Welsh and English myth, the queen of the fairies, subsequently shorn of that supremacy by Titania (q.v.).  The name is from the Erse Meubhdh, which is said to have belong originally to a great Irish princess.  Beaufort, in his Ancient Topography of Ireland, mentions Mabh as the chief of the Irish fairies.  Shakspear puts a famous description of her into Mercutio's mouth in Romeo and Juliet, i, iv, 55.  He is the first to call Mab the queen of the fairies.  He additionally describes her as "the fairies' midwife," because, as T. Warton surmises, she steals new born infants and leaves changelings in their place.  Steevens on the other hand explains that she is so called because it was her task "to deliver the fancies of sleeping men of their dreams,—those children of an idle brain."  In Milton's L'Allegro (l. 103) Mab has cast aside her regal dignity and reassumed her original and humbler role of a teasing and mischievous sprite, whose petty annoyances punished slothfulness and slovenliness in maids, and who deigned to accept their propitiatory offerings of junkets set out at night for her delectation. 
    Shelley's Queen Mab, in a poem of that name (1810), is ruler over a fairy court, far beyond the confines of the earth, whither the soul of Ianthe is borne in a dream, so that she may be converted from the errors of revealed religion. (Heroes and Heroines of Fiction, vol. 2, Classical, Mediaeval, Legendary, Walsh, 1915).