"The unauthorized use or close imitation of the language and thoughts of another author and the representation of them as one's own original work."
From The Random House Dictionary of the English Language, 2d ed.
If Val copies someone else's words into her paper and she does not give the original author appropriate credit for his or her work, she is plagiarizing. Val is stealing the hard work of another person and passing it off as if it were her own effort.
The bottom line: Using an author's words, thoughts, or ideas without giving credit is plagiarism.
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