What is plagiarism?
Plagiarism is the action or practice of taking and presenting the thoughts, writings or other work of someone else as though it is your own work. It is different to copyright infringement, but one may also involve the other depending upon the situation. If you do not give proper attribution to the author of material you may also breach moral rights, which have separate protection under the Copyright Act 1968.
While copyright infringement and plagiarism are not the same thing, there may be situations where the two will overlap. Using other people's published work in an academic assignment may be plagiarism (if it is used without proper reference) but it may not be an infringement of copyright, if for example it has been used by a student under the exception for fair dealing for the purposes of research and study.
However, if a student copied a complete poem for example and submitted it for assessment as their own work, that is likely to constitute both copyright infringement and plagiarism.
What are the possible consequences?
Plagiarism and copyright infringement have different outcomes. The penalty for plagiarism is usually a disciplinary matter administered internally by the university under its own policies and procedures. A copyright owner can take legal action in the courts against a party who has infringed their copyright.