A binder is a folder with metal rings that hold loose papers together. The rings open and close with a snap, letting you add or remove pages easily. Students use binders to organize handouts, homework, and notes for different subjects. You might have a binder for math with dividers separating classwork, tests, and practice problems.

Binders come in different sizes: one-inch, two-inch, or even larger for big projects. The rings let you keep everything in order without papers falling out like they might from a regular folder. Many students prefer binders because they can reorganize pages, add new material anywhere, and use hole-punched pockets for supplies.

The word can also mean someone who binds things together professionally, like a bookbinder who crafts and repairs books. In farming and construction, a binder might refer to a substance or tool that holds materials together, such as the binder in concrete that makes it harden into solid material.