This is the number of sides a polygonal pot has. If this value is two or more, the polygon effect is enabled and the pot is polygonal. If it's less than two, the polygon effect is disabled and the pot is circular.
The number of sides can be fractional. An integer number of sides produces a regular polygon, whereas a fractional number of sides produces a polygon with one side shorter than the others. The number of sides can be modulated for interesting effects, but don't let the modulated value go below two, otherwise invalid geometry results.
To round the polygon's corners, use Polygon Roundness. To bulge or pinch the polygon's sides, use Polygon Bulge.