What does 8 mesh screen mean when it's referenced in a description of an Air Vent roof louver?

8 mesh screen means for every square inch of screen there are 8 squares horizontally and 8 squares vertically so as to indicate the frequency of the screening.

This is what it means: for every square inch of screen there are 8 squares horizontally and 8 squares vertically so as to indicate the frequency of the screening.