The left edge of a sheet protector (punched pocket)

word-choice single-word-requests american-english british-english

I see several similar product-description pages that refer to the reinforced strip/side as the binding edge. I suggest punched binding edge. This, of course, is the edge that goes into a loose-leaf binder.

Each binding edge is 11-hole punched to ensure they are compatible for any binder or presentation cover. Google Shopping

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