When printing, collate means that if you’re printing multiple copies of a multi-page document, the printer will organize the pages in the correct order for each copy. For example, if you print three copies of a 3-page document with collate on, you’ll get: 1-2-3, 1-2-3, 1-2-3. If collate is off, the printer prints all copies of page 1 first, then all copies of page 2, and so on (1-1-1, 2-2-2, 3-3-3). It’s basically about keeping the pages in order for each set.