* When it refers to a specific group of singers: This is the most common usage. For example, "The Chorus sang beautifully."
* When it's part of a proper noun: This could be the name of a specific choir, like "The Chorus of the Metropolitan Opera."
* When it's the first word of a sentence: This is a basic rule of grammar.
You would not capitalize "chorus" when:
* It's a general term for a group of singers: "The play featured a large chorus."
* It's used as a synonym for "refrain": "The song's chorus was catchy."
Remember, the capitalization of words is often determined by context. Pay attention to the specific meaning and usage within the sentence.