A nondimensional number arising in problems of a rotating viscous fluid, written as T =(f²h⁴)/v², where f is the Coriolis parameter (or, for a cylindrical system, twice the rate of rotation of the system), h the depth of the fluid, and v the kinematic viscosity; the square root of the Taylor number is a rotating Reynolds number, and the fourth root is proportional to the ratio of the depth h to the depth of the Ekman layer.