The term 'THEY'RE USED MOSTLY ON CORNERS' is referring to staplers, which are 8-letter tools used to join two or more pieces of paper together. Staplers are most commonly used in offices and schools, but can also be found in homes. They are usually used to secure documents, such as reports, presentations, and other important papers. Staplers are typically used on the corners of the paper, although they can also be used in the middle of a page.