Plagiarism is when you pass someone else's work off as your own. It can be intentional or unintentional.
Plagiarism is the act of passing off concepts or content that have been produced previously as new, original work. In practical terms, in academic writing, this usually means quoting or paraphrasing the work of other scholars without proper citation. See the Rosemont Student Handbook for a full definition of what is considered plagiarism by the College and a description of its consequences.
Every student has a responsibility to be attentive to citation concerns. Ignorance is no excuse, and unintentional plagiarism is still a serious academic offense.
If you reuse work that has been submitted for a previous class to satisfy a current class requirement (or republish work that has already appeared without indicating that fact), it still constitutes plagiarism and will be treated accordingly.