Appropriateness is whether something fits the time, the place, the people, and the purpose. A joke can be funny and still fail this test at a funeral. Clothes, words, gifts, and even silence can be judged this way. The question is not only is this nice? but is this right for this situation? You will meet the word in school rules, workplaces, and talk about manners. Though actually, the answer is not the same in every room or every culture: what is fine with friends may be wrong in a meeting. This noun comes from the adjective appropriate (suitable), not from the verb appropriate (to take something for yourself).