The Blue Stockings Society was an informal women's social and educational movement in England in the mid-18th century, created in imitation of the French society of the same name, but emphasizing education and mutual co-operation rather than the individualism which marked the French version.
The Society was founded in the early 1750s by Elizabeth Montagu and others as a women's literary discussion group, a revolutionary step away from traditional non-intellectual women's activities. They invited various people to attend, including botanist, translator and publisher Benjamin Stillingfleet. One story tells that Stillingfleet was not rich enough to have the proper formal dress, which included black silk stockings, so he attended in everyday blue worsted stockings. The term came to refer to the informal quality of the gatherings and the emphasis on conversation over fashion. (from Wikipedia, Blue Stockings Society)
Mrs. Montagu (see wiki article quoted above) may have been source material for Lady Smatter. (According to Betty Rizzo, Mrs. Montagu gave a rather poor review to Frances Burney's novel.) This women's intellectual society was in theory about the free exchange of ideas -- but of course all exclusive societies have their own "status" rules. Later "Bluestocking" became an insulting term for an intellectual woman (i.e., probably not pretty or marriage material, a nerd, a lesbian, etc.)
Interesting that Cecilia does not see herself as a potential member of the Esprit Party-- she may be playing her own status game by declaring that she is not the sort of woman who would join that sort of club (i.e., pretty and marriage-bound).
-- Erika Iverson