The Collaborative International Dictionary of English v.0.48:

Folder \Fold"er\, n.
   One who, or that which, folds; esp., a flat, knifelike
   instrument used for folding paper.
   [1913 Webster]

WordNet (r) 3.0 (2006):

folder
    n 1: a small book usually having a paper cover [syn: booklet,
         brochure, folder, leaflet, pamphlet]
    2: covering that is folded over to protect the contents

The Free On-line Dictionary of Computing (19 January 2023):

directory
directories
folder

    A node in a hierarchical file system which
   contains zero or more other nodes - generally, files or
   other directories.

   The term "folder" is sometimes used in systems such as the
   Macintosh or Microsoft Windows in which directories are
   traditionally depicted as folders (like small briefcases).

   (2007-02-21)