If a student submits an assignment that contains work that is not their own, without indicating this to the marker (acknowledging your sources), they are committing ‘plagiarism’ and this is an offence.
Submitting work that has been done by someone else and persistent borrowing of other people’s work without citation are obvious instances of plagiarism and are regarded as cheating. Copying answers from social networking sites is cheating. Paying for work from other sources and submitting it as your own is also cheating. It is intellectually dishonest to cheat and thus give one student an unfair advantage over others.
Passing on an assignment to others, with the knowledge that another student may plagiarise the assignment will also lead to a penalty.