It's called benday.
From Wikipedia;
The Ben Day process is a printing and photoengraving technique for producing areas of gray or (with four-color printing) various colors by using fine patterns of ink on the paper. It was developed in 1879 by illustrator and printer Benjamin Henry Day Jr. (son of 19th-century publisher Benjamin Henry Day). The process is commonly described in terms of Ben Day dots, but other shapes can be used, such as parallel lines or textures
IMO if you're going to use it, use it consistently.