Term for a crossword's grid "density"?

A crossword puzzle's (usually square) grid has white squares and black squares. I define a crossword grid's "density" to be the ratio of the number of white squares to the total number of squares. Clearly, the larger the density the harder the crossword will be to construct, with a ratio of one being a grid with no black squares at all.

For example, a recent New York Times crossword is a 15-by-15 square with 42 black squares and 225-42=183 white squares for a "density" of 183/225, approximately 0.81.

Is there a term of art for what I am calling crossword puzzle density? If so, can someone provide a source for that term?

• In linear algebra, the term density refers instead to the ratio of the number of nonzero elements to the total number of elements (not to the number of zero elements). May 8 at 2:16
• You don't distinguish between checked white squares (where an Across and a Down cross) and unchecked ones. Is this what you intend? Checked ones make constraints that unchecked ones do not, and thus make it harder to fill the grid.. May 8 at 5:18
• @RosieF most american crosswords (including nyt crosswords) have no unchecked white squares May 8 at 17:00
• @RobPratt is correct and I have changed the question to reflect his suggestion. May 8 at 17:48