Plagiarism: what is it?

The UGent Education and Examination Code defines plagiarism as follows: "to commit plagiarism is to present (parts of) a source as original and your own, without adding any acknowledgements."

You can read more about this in the guide about academic writing by the Faculty of Arts and Philosophy, in particular this page about plagiarism. You can also have a look at the pages about paraphrasing and citing & quoting.