folder

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. One that folds or is folded, such as a booklet or pamphlet made of one or more folded sheets of paper.
2. n. A flexible cover folded in the center and used as a holder for loose paper: a file folder; a hanging folder.

Century Dictionary and Cyclopedia

1. n. One who or that which folds; specifically, a flat knife-like instrument, frequently of bone or ivory, used in folding paper.
2. n. A circular, time-table, map, or other printed paper folded in such a way that it may be spread out in one sheet.
3. n. In entomology, one of many insects which fold leaves: as, the grape-leaf folder. See Desmia and leaf-folder.
4. n. An attachment to a sewing-machine for bending and folding the fabric previous to sewing. It is made in a great variety of forms to produce the different plaits, folds, and bands used in garment-making and in decorative sewing.
5. n. In sheet-metal work, a hand-power machine for folding over the edges of sheet-metal plates to form a lock, turning the edges of small tinware and roofing-plates, etc.: a tin-folding machine.

Wiktionary

1. n. An organizer that papers are kept in, usually with an index tab, to be stored as a single unit in a filing cabinet.
2. n. computing A virtual container in a computer's file system, in which files and other folders may be stored. The files and subfolders in a folder are usually related.
3. n. A machine or person who folds things.

GNU Webster's 1913

1. n. One who, or that which, folds; esp., a flat, knifelike instrument used for folding paper.

WordNet 3.0

1. n. a small book usually having a paper cover
2. n. covering that is folded over to protect the contents