What is the definition of plagiarism?
According to BBC English Dictionary (Harper Collins Publishers, 1992) plagiarism is "the practice of using or copying someone else's idea or work and pretending that you thought of it or created it". The word is also "used showing disapproval".
More definitions can be found in Google. Write 'define:plagiarism' (without quotes) in Google's search box.
You can found article on plagiarism in Wikipedia: http://en.wikipedia.org/wiki/Plagiarism.