Plagiarism is the act of presenting someone else's work as your own. It is the theft of intellectual property.
It is also sometimes known as "cutting & pasting", especially with information obtained from sources found on the Internet.
Avoiding plagiarism
It is really important that you avoid plagiarism. Here are some resources that you can use to help you accomplish this task.
Plagiarism & Academic Integrity
This engaging interactive site from Rutgers University’s Scholarly Research Communication Center is a good starting point for a discussion about plagiarism.