What is the primary feature of something described as 'boisterous'?

The term 'boisterous' primarily refers to loud, energetic, and exuberant behavior. When something is described as boisterous, it typically indicates a sense of lively excitement, often marked by cheerfulness and high spirits. This aligns perfectly with the chosen answer, which highlights exuberance as a key aspect of being boisterous.

The other options represent characteristics that are contrary to the essence of boisterousness. For instance, quietness suggests a lack of sound or activity, while calm demeanor implies a peaceful and tranquil atmosphere. Chaotic behavior, while suggesting a lack of order, does not necessarily capture the joyful and spirited connotation of boisterousness. Therefore, exuberance stands out as the most fitting description of the primary feature of something described as 'boisterous'.