What do you call a 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 sided polygon?

Answer 1

Were such a figure to be inscribed upon a plane such that the longest diameter of the object was equal to the extent of the visible universe, the sides would be far smaller than the diameter of a proton. Such an object would be, for all practical purposes, a circle, and any smaller copy would approach a circle even more closely.