Fair-use is a legal boundary that protects freedom of expression by permitting unlicensed use of copyrighted works in certain circumstances. If fair use is in place, it is mostly in the instance that it is being used for educational or creative purposes, not to be sold or capitalized off of. If something is copyrighted, unless a fair-use policy is in place, you may not use the work in any circumstance unless granted a license.

Copyright.Gov - US Copyright Office

NYU - Copyright