Tearful describes someone who is crying a little, or is right on the edge of it — eyes wet, voice shaking, not yet sobbing. That 'not yet' is the heart of the word. If someone is crying hard, you say they are crying; 'tearful' is for the quieter state just before or just after, and it is gentler and more polite than saying 'she was crying', which is why news reports and careful writers like it. It also describes occasions and things, not only people: a tearful goodbye, a tearful phone call, a tearful reunion at the airport. There it means the event had crying in it — and note that this is not always sadness. A tearful reunion is a happy one; the tears are from feeling, not from unhappiness. Which feeling it is comes from the situation around the word, not from the word itself.