1. Is it for a nonprofit or educational purpose?
2. What kind of material is it?
3. Are you using only a small portion?
4. Will your use deprive the author from making money?
Copyright
the exclusive right to make copies, sell, or otherwise profit from a literary, musical, or artistic work, whether printed audio, video, etc. Copyright protection lasts for the lifetime of the creator plus a period 70 years after his or her death.
Creative Commons
a license that allows the creator of a work to decide which rights they will keep and which they will share with others (example: noncommercial reuse, reuse with modification, etc.).
Fair Use
the right of the public to make fair or reasonable use of copyrighted material in special circumstances without the copyright owner's permission. Fair or reasonable uses include criticism, parody, news reporting, teaching, and research.
Plagiarize
to steal and pass off another person's work as your own; to use someone else's work without crediting the source.
Public Domain
not covered by copyright; widely available to the general public.