Answer : Points
Explanation : A plane is a set of points on a flat surface that extends forever.
The definition of the plane is "In mathematics, a plane is a flat, two-dimensional surface which extends infinitely far. A plane is the two-dimensional analogue of a point (zero dimensions), a line (one dimension) and three-dimensional space."
It clarifies that the above answer is correct as the correlation of a line, point and segment in a three dimensional space or a flat surface is called as a "Plane."
Therefore, it is clear that the answer is a set of points is the factor which defines a plane.
