http://mathworld.i2p/Q.html
It derives from the German word Quotient , which can be translated as " ratio. " The symbol first appeared in Bourbaki's Alg è bre (reprinted as Bourbaki 1998, p. 671). See also C , C-* , Field of Rationals , I , N , Q-+ , Q-Bar , Q-Function , q -Product , q -Series , R , Z References Bourbaki, N. É l é ments de math é matique: Alg è bre. Reprinted as Elements of Mathematics: Algebra I, Chapters 1-3.