Used about love, or another strong feeling, that you give to someone who does not give it back. You love them; they do not love you. The word almost always sits in front of 'love' — 'unrequited love' is by far the most common way you will ever see it, so common that many people have never met the word anywhere else. You can also say unrequited affection, unrequited longing, unrequited passion. It is a written, literary word: you meet it in novels, songs, film reviews and sad essays, not really in ordinary talk. A friend telling you about their heartbreak would say 'he doesn't feel the same way' — they would not say 'my love is unrequited' unless they were being a little poetic, or joking about being dramatic. Note that it does not mean the feeling is secret. You may have told the person; you may have been turned down clearly. What makes it unrequited is only that the other side is empty. And note that it is not about being rejected once — it names a state that goes on, a feeling you keep carrying alone. People also stretch it a little away from love: 'unrequited loyalty' to a company that does not care about you, an 'unrequited' friendship where only one person makes the effort. Those uses are less standard but people understand them straight away.