Explanation:

- The Notting Hill Carnival is a vibrant event known for its colorful parades.

- Costumes: Participants commonly wear themed costumes to express the cultural and artistic aspect of the carnival.

- Clothings: Generally a broader term that does not specifically refer to themed or festival attire.

- Apparels: Like "clothings," it’s a broad term but isn’t often used to describe specific festive outfits.

- Dressing: Generally refers to the act of putting on clothes and is not typically used for themed outfits.

Correct Answer: Option 2 - costumes