撮 is a classifier used for a tuft or small bunch of hair, grass, or fibrous material — think of a lock of hair or a clump of grass. It can also be used figuratively for a small group of people (e.g., 一撮坏人). The standard pronunciation is cuō (first tone), though in Taiwan it is sometimes pronounced cuò (fourth tone). Use it when you want to describe something that naturally forms a small bundle.