joy: glad rejoicing, and by extension the person or place that is someone's delight
This is a heightened, poetic word for joy. It is not the everyday word for being happy but the language of festival, celebration, and prophetic vision, and it clusters in Isaiah and in the songs of mourning where its loss is felt most sharply.
It runs along two lines that flow into each other. Most often it names gladness itself: the sound of music, the exultation of a wedding, the delight of the heart. But it just as naturally names the thing that stirs that gladness, so that a city can be called "the joy of the whole earth" (Psalm 48:2), meaning the place everyone delights in. English does the same thing when we call a person "my pride and joy," and this word moves easily between the feeling and its object.
Because it is so tied to celebration, it is a word the prophets love to take away. When judgment falls, the music stops and the joy is silenced; when God restores his people, he creates joy where there was mourning. It belongs to the same family as שָׂשׂוֹן, a close companion word for gladness, and overlaps the far more common everyday term שִׂמְחָה.