Final answer:
The secular vocal composition for three or more voices popularized by Adrian Willaert during the Renaissance is the madrigal. This form was notable for its polyphonic texture and expressive lyrics, and it represents a key genre of secular music from that era.
Step-by-step explanation:
The secular vocal composition for three or more voices, made popular by Adrian Willaert, is known as the madrigal. During the Renaissance, this Italian genre of music found immense popularity and was characterized by its use of canons and polyphony. A notable shift in music during the early Renaissance was the increased reliance on the interval of the third, making the music sound smoother and allowing for more intricate polyphonic arrangements. Secular music included a variety of forms, among which the madrigal stood out for its complex interweaving of vocal parts and emotional expressiveness.
Adrian Willaert played a significant role in popularizing the madrigal, which became a prominent form of secular music alongside others like the German Lied, French chanson, and Spanish villancico. The Renaissance period also saw sacred musical forms like masses and motets being influenced by secular genres, indicating a fusion and evolution in musical styles.