Have you plagiarized?
It is plagiarism when you:
Use four or more significant words or ideas of another person without citing them
Summarize or paraphrase words or ideas of another person without citing them
Borrow facts, statistics, or other material, unless the information is common knowledge
Buy or use a term paper written by someone else
Cut and paste passages from the Web, a book, an article, or other publication and insert them into your paper without citing them
As you can see, plagiarism ranges from copying word-for-word to paraphrasing a passage without credit and changing only a few words.