PlotDivision is an option for Plot which specifies the maximum amount of subdivision to be used in attempting to generate a smooth curve.
Plot initially uses PlotPoints equally spaced sample points. In attempting to generate curves with no bends larger than MaxBend, Plot subdivides by at most a factor of PlotDivision.
The finest resolution in Plot is of order 1/(PlotPoints PlotDivision).
See The Mathematica Book: Section 1.9.3.
See also: MaxBend.