The gradient determines the colors of the turbulence.
U Frequency and V Frequency determine the fineness of the structure. U=1 and V=1 create a radial-like pattern, while U=1 and V=0.25 give elongated shapes. The higher these values, the greater the detail (or frequency) in the relevant direction.
Octaves is the number of iteration steps for generating this fractal turbulence. The more octaves, the more added detail you obtain. With a setting of 1, the Turbulence shader is almost identical to the Noise shader; there is no point in setting this value too high since only a certain amount of detail can be added.