Copyright  

Noun: The exclusive legal right, given to an originator or an assignee to print, publish, perform, film, or record literary, artistic, or musical material, and to authorize others to do the same.

When Do I Need to Ask Permission?

If your work contains copyrighted material, and you have not obtained permission from the owner of the work, it can only be used if:
(i)  the material is in the "public domain" (i.e. out of copyright);
(ii)  the material is uncopyrightable (e.g., unadorned ideas are common property);
(iii) the work is subject to a "Creative Commons" license; or
(iv) the proposed use is a "fair use."