In general, plagiarism can be defined as the unacknowledged use of the work of others as if this were your own original work.
In the context of an examination, such as that for the MPhil or PhD, this amounts to passing off the work of others as your own to gain unfair advantage.
The Department and University take the issue of plagiarism very seriously.
It is crucial that throughout your time as a graduate student you adopt practices that avoid the unacknowledged use of the work of others. This is true for all of your work including reports and your final dissertation. The ready availability of large amounts of text on the WWW represents a particular danger.
Useful information is available on the 'Good academic practice and plagiarism' webpages, and the matter is dealt with in detail in the Code of Practice for Research Degrees. If in any doubt, seek advice.
Note that such use of unfair means will not be tolerated by the University; if detected the penalty could be severe and may lead to failure to obtain your degree.