There are some actions that can almost unquestionably be labeled plagiarism. Some of these include buying, stealing, or borrowing a paper (including, of course, copying an entire paper or article from the Web); hiring someone to write your paper for you; and copying large sections of text from a source without quotation marks or proper citation.
But then there are actions that are usually in more of a gray area. Some of these include using the words of a source too closely when paraphrasing (where quotation marks should have been used) or building on someone's ideas without citing their spoken or written work. Sometimes teachers suspecting students of plagiarism will consider the students' intent, and whether it appeared the student was deliberately trying to make ideas of others appear to be his or her own.
Here are some links to website to help you understand and avoid PLAGIARISM;