Longman Dictionary of Contemporary English
Wiktionary
n. A folder in which punched pieces of paper may be held by means of clamps running through the holes in the paper.
Wikipedia
Ring binders (loose leaf binders, looseleaf binders, or sometimes called files in Britain) are large folders that contain file folders or hole punched papers. These are held in the binder by circular or D-shaped retainers, onto which the contents are threaded. The rings are usually spring-loaded, but can also be secured by lever arch mechanisms or other securing systems. The binders themselves are typically made from plastic with metal rings. Early designs were patented during the early 1890s to the early 1900s.
Usage examples of "ring binder".
You just have to find a sufficiently virulent business plan, condense it into a three-ring binder-its DNA-xerox it, and embed it in the fertile lining of a well-traveled highway, preferably one with a left-turn lane.
This one is carrying a three-ring binder with the Buy 'n' Fly logo.
I've run out of pink invoice paper, so three-ring binder paper from the Staples across the street will suffice.
The outline for the operation was contained in a fat three-ring binder, the Monthly Reconnaissance Schedule for January 1968.
He had to open a three-ring binder and root through it until he found the storage site inside the big communications vault at the far corner of the room.
There was the faceted red stone the size of an egg, a gold chalice etched with strange symbols, and a blue three-ring binder.
Beside the water bag lay her schoolwork, represented by a three-ring binder suffering the indignities of artificial bit-rot, its wire-frame cover festered with digital mung.