noun-plural. A state of depression or melancholy. Often used with the.noun-plural. A style of music that evolved from southern African-American secular songs and is usually distinguished by a strong 4/4 rhythm, flatted thirds and sevenths, a 12-bar structure, and lyrics in a three-line stanza in which the second line repeats the first: "The blues is an expression of anger against shame and humiliation” ( B.B. King).