Wikipedia
Disc-binding is a type of notebook binding that uses discs to hold the sheets of paper. Each disc has a raised edge. Notebook sheets have perforations along the binding edge that match the profile and spacing of the binding discs.
Notebook sheets are removed by peeling the perforations away from the binding discs. Sheets are added by affixing the perforations to the discs. Sheets can be transferred between disc-bound notebooks of different functions and sizes, provided the discs have the same profile and spacing. In addition to using paper specifically manufactured for a particular disc-binding system, ordinary paper can be inserted by using a specially designed hole punch to perforate the pages to conform to the discs.
Several companies have manufactured or distributed disc-binding systems. These include the Belgian firm Atoma, the now-defunct Israeli brand Flic, Levenger Company (under the brand name Circa) in the US, Clairefontaine (under the brand 'Clairing') in France, Rollabind in the US, Office Depot (TUL), Staples (Arc), and William Hannah in the UK.