Fair Use means under certain circumstances it is allowable to use part of a copyrighted work. Fair use is what allows people to make parodies, quote sections of a book in a book review, or copy articles for research.
There are four factors that can be used to determine whether something is more or less likely to be considered fair use.
They are:
1. Purpose and character of the use
2. Nature of the source
3. Amount of the source used
4. Effect on the market
Courts may also consider whether the use is transformative (whether it add something new or does something different from the original). If you applyi these factors to your intended use of a copyrighted work it can demonstrate that you are acting in good faith. Actual decisions on fair use are only made after a rights holder has sued over copyright infringement.