affine hull

The affine hull of a set of points is the smallest possible flat surface (like a line, plane, or higher-dimensional analogue) that contains all those points. Imagine stretching a rubber band around a set of pegs on a board; the shape the band forms represents the affine hull—it's the minimal "flat" shape that includes all the points. It considers all linear combinations of the points where the sums of the coefficients add up to one, ensuring the shape maintains the same overall dimension as the points' configuration.