The definition of copyright is basically the right to copy. To use someone's art, music, or anything, you must have permission to use their work. Otherwise, they are the only people with the right to reproduce from their work. Copyright certificates can be used as a layer of protection over a person's effort on their work. Breaking the law of copyright can lead to serious consequences.
Fair use is a form of copying and copyrighting for an acceptable purpose. This could mean using it for comments, criticism, or another form of the work itself. Understanding the concept of using fair use for an acceptable purpose is a broad understanding. It has few limits and is up for interpretation, which is what it was meant for. This prevents areas where there could be consequences.
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Copyright
Fair Use