The Collaborative International Dictionary of English v.0.48:

looseleaf binder \looseleaf binder\, looseleaf notebook
\looseleaf notebook\n.
   A type of notebook with hard covers attached to metal rings
   which open, allowing sheets of writing paper to be
   conveniently inserted into it and removed from it.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Binder \Bind"er\, n.
   1. One who binds; as, a binder of sheaves; one whose trade is
      to bind; as, a binder of books.
      [1913 Webster]

   2. Anything that binds, as a fillet, cord, rope, or band; a
      bandage; -- esp. the principal piece of timber intended to
      bind together any building.
      [1913 Webster]

   3. a pair of stiff oblong covers, sometimes detachable,
      designed for insertion of paper pages to create a
      book-like document, such as in a loose-leaf binder.
      [PJC]