N.E.W.T.s (Nastily Exhausting Wizarding Tests)
are subject-specific exams that seventh-year wizards and witches at Hogwarts take to help them get certain jobs after graduation. For instance, the Ministry of Magic only accept Auror applicants with at least five N.E.W.T.s with the grade "Exceeds Expectations" or better. Not all wizards pass or even take the N.E.W.T.s, as they can find other jobs using their O.W.L. results. Fred and George Weasley, for example, were not bothered about taking the N.E.W.T.s and left Hogwarts in the middle of school-term (since their ambition was to open their joke shop, results were not an imperative in their opinion).
A student must have previously achieved an O.W.L. in the subject in order to move on to N.E.W.T.-level classes. Many Hogwarts Professors will accept an "Exceeds Expectations" in the student's O.W.L. for a class in order to allow them into the N.E.W.T.-level classes; however, some, such as Severus Snape, would only let students with an "Outstanding" in their O.W.L. pass through to his Potions N.E.W.T. class.