Today is Public Domain Day, which is designated to celebrate the role of public domain in our culture by highlighting authors who died in 1941 and whose work will enter the public domain on 1 Jan 2012.
A little fuzzy on the concept of public domain? When an author’s copyright expires, his or her works enter the public domain where they can be used for any purpose without prior permission.
Copyright usually extends from the life of the author plus a certain number of years after his or her death (or pma: post mortem auctoris). In the United States and the European Union, the copyright terms for authors expire 70 years pma; in Canada and New Zeland, copyright ends 50 years pma.