How is a copyright different from a trade secret?
The underlying purpose of trade secret law is to protect information which is kept secret and out of the marketplace if it gives its owner a commercial advantage. Copyright law, on the other hand, protects original information created by an author. While copyrighted information is generally disclosed to the public (not only is it generally published, displayed or performed, but copies are required to be publicly deposited with the Copyright Office of the Library of Congress), trade secret information is generally not disclosed to the public, because then the information loses the right to be protected as a trade secret.
However, information can be protected by both a trade secret and copyright in certain situations. In particular, where a portion of a work is not entitled to copyright protection but is eligible for trade secret protection, the author may redact the trade secret portion from the work before depositing it with the Copyright Office. The most obvious example of such a situation would be something like a computer program which uses algorithms and mathematical equations which are not entitled to copyright protection.