A proprietary format ("closed" is sometimes used as a synonym for "proprietary") is a format (i.e. data structure, protocol, or other data storage/transfer standard) which is considered to be intellectual property and may not be used without the consent of the format's owner (usually given in the form of a license). This often prevents or severely hampers efforts to be able to read or write data stored in those formats in free software due to a number of factors, including licensing requirements typically imposed by owners of such formats.
Examples of closed formats include: MP3, WMA, Microsoft Word .doc format, Microsoft Excel .xls format (both of the latter are in fact readable by a number of free software programs; the main problem there is the poor documentation of the format, not licensing restrictions).
- 2002-01 We Can Put an End to Word Attachments by RIchard M. Stallman