Can I quote a sentence from another paper? I am writing a paper and I have found in another paper a definition for a quantity which I am working with that is very clear and is written much better than I will ever be able to do. I tried paraphrasing it, but the result is not so clear: can I quote it in my paper?
You can quote it as long as you reference it properly.

If you do not provide the source then that is plagiarism.