MaxBend is an option for Plot which measures the maximum bend angle between successive line segments on a curve.
Plot uses an adaptive algorithm to try and include enough sample points so that there are no bends larger than MaxBend between successive segments of the plot.
Plot will not, however, subdivide by a factor of more than PlotDivision.
Smaller settings for MaxBend will lead to smoother curves, based on more sample points.
See The Mathematica Book: Section 1.9.3.