What is not covered by copyright?

Although most information is protected by copyright, there is an exception. Works within the public domain can be reproduced or used by anyone. Even though you can use these materials for free, you still must credit the author by citing your sources. 

Here are examples of public domain sources:

Public Domain Sources Examples
Publications of the U.S. Government  U.S. laws and other publications of the Federal government, the U.S. Constitution

Copyright has been waived by the author

Software called freeware

Works on which the copyright has expired

(written before 1923)

Works by William Shakespeare