Halftone screen
From The Glossary of Digital Photography
A glass or film screen that has a pattern of fine lines etched in it, typically at a rate of 50 to 200 lines per inch. When an image is photographed through these lines using a high-contrast film, it is broken up into very fine dots that are easier for a printing process to reproduce. The size and shape of the dots is by determined the type of screen used.
