Final answer:
A composition with melody in more than one line simultaneously is called polyphony. This complex musical texture interweaves multiple independent melodic lines, typical in many genres and historical periods.
Step-by-step explanation:
A composition that involves melody in more than one line simultaneously is called polyphony. Polyphony is a term that emerged during the Renaissance and has played a significant role in the development of Western music. This musical texture involves multiple independent melodic lines being played or sung at the same time, creating a complex and harmonious sound. Composers construct these lines so that they intertwine yet retain their individuality, creating a rich tapestry of sound. Polyphonic music can be heard in various genres and styles, from classical choral works to contemporary instrumental music.