der Binder
binder
A file binder or folder with a ring mechanism for filing punched sheets of paper.
Bitte hefte die Rechnungen in dem blauen Binder ab.
Please file the invoices in the blue binder.

binder
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binder
A file binder or folder with a ring mechanism for filing punched sheets of paper.
Bitte hefte die Rechnungen in dem blauen Binder ab.
Please file the invoices in the blue binder.

'Der Binder' (the binder) comes from the verb 'binden' (to tie). The suffix '-er' often refers to a tool or a person that performs an action. So a 'Binder' is something that binds or holds things together.
Ich brauche einen großen Binder, um alle meine Unterlagen zu ordnen.
I need a large binder to organize all my documents.
You can recognize the meaning from the context. In the office or at school, it means a file binder. In cooking or construction, it means a binding agent. In connection with clothing, it means a tie.
Die Dokumente für die Versicherung sind in dem roten Binder.
The documents for the insurance are in the red binder.
The use of 'Binder' for a tie is outdated or colloquial. In most situations today, the word 'Krawatte' (tie) is used.
Mein Großvater nannte seine Krawatten immer „Binder“.
My grandfather always called his ties 'Binder'.
folder / binder / steward
'der Ordner' and 'der Binder' can both mean an object in which you file punched sheets of paper. 'Ordner' is very common in everyday German in Germany and usually means the classic file binder with a ring or lever mechanism. 'Binder' can mean something similar, but depending on the region or context it sounds less everyday. Also, 'Binder' has other meanings that are not meant here. The words can be confused because both hold paper together. If you are talking about filed documents at the office or at school, 'Ordner' is usually the more natural choice.

Die Anleitung liegt in einem schmalen Binder neben dem Drucker.
The instructions are in a narrow binder next to the printer.
Für den Deutschkurs brauche ich einen Ordner mit Registerblättern.
For the German course, I need a binder with dividers.