AbsolutePointSize[d] 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, AbsoluteThickness, Thickness.