] is a graphics directive which specifies that points which follow are to be shown if possible as circular regions with absolute diameter d.
The absolute diameter is measured in units of printer's points, approximately equal to of an inch.
AbsolutePointSize can be used in both two- and three-dimensional graphics.
See the Mathematica book: Section 2.9.3.
See also: Offset, PointSize, Thickness.
The point size of the points on the diagonal range from to printer's points; the circled point is shown at the default point size.
Evaluate the cell to see the graphic.