The answer is the madrigal.
The galliard was a lively dance form popular in the Renaissance period, characterized by its triple meter and energetic steps. While it was significant in the context of dance music, it was not the most important secular genre of the sixteenth century.
The chanson was a popular French secular vocal music form during the Renaissance. It was significant and widely appreciated, but it did not have the same widespread influence and development as the madrigal.
The madrigal was the most important secular genre of the sixteenth century. Originating in Italy, it became highly popular across Europe. Madrigals were known for their expressive text settings, intricate counterpoint, and emotional depth. They were performed in various social settings and had a significant impact on the development of secular music during the Renaissance.
The ronde, or round dance, was another form of dance music. While it was popular, it did not achieve the same level of importance or influence as the madrigal in the context of secular music genres.