GraphicsSpacing is an option for GraphicsArray which specifies the spacing between elements in the array.
GraphicsSpacing -> 0 inserts no horizontal or vertical spacing, so that all adjacent rectangular areas in the array are shown abutting.
GraphicsSpacing -> h, v specifies horizontal and vertical spacing to use.
GraphicsSpacing -> s is equivalent to GraphicsSpacing -> s, s.
The spacing is given in scaled coordinates, relative to each rectangular area in the array.
Example: a horizontal spacing of 0.1 yields an array in which the rectangular areas are separated horizontally by distances equal to 0.1 of their widths.
See The Mathematica Book: Section 1.9.4.
See also: TableSpacing.