Plagiarism is 'to steal and pass off (the ideas or words of another) as one's own' or 'use (another's production) without crediting the source' (Merriam-Webster Dictionary).
See Authenticity and Academic Integrity: A Guide from TASC for more information.
For a good explanation of what plagiarism is and how to avoid it, look at Plagiarism.org.
Find great additional information and resources located in the fronter module on Academic Integrity.
To access these resources just enter flexible (username) and flexible (password).
You will find three strands in this module covering academic integrity, referencing, copyright and ownership.
Most information is located in the Resources folder to the left of the screen.