Fair use is a legal concept that allows the reproduction of copyrighted material for certain purposes without obtaining permission and without paying a fee or royalty. Purposes permitting the application of fair use generally include review, news reporting, teaching, or scholarly research. The idea of fair use originally arose for written works. But with the advent of digital technology and the Internet, fair use has sometimes been applied to the redistribution of musical works, photographs, videos, and computer programs.
The limits of fair use are not always clear. Fair use may (but does not always) include the reproduction of a song or photograph to give to a single relative or friend as a gift. If you intend to make a profit by reproducing and reselling a copyrighted work or part thereof, that does not normally constitute fair use. Other factors include the size or extent of the passage or material reproduced, the length of time for which the material will be used, the number of copies of the reproduced work that will be distributed, and the effect of the use on the market value of the original copyrighted work.
Anyone in doubt about whether a given activity constitutes fair use of a copyrighted work should consult an attorney. It may be faster and simpler to request permission of the copyright owner.