奶盖 (literally 'milk lid') is the salty whipped cheese-cream layer that floats on top. Originated in Taiwan in the early 2010s and became a staple at chains like 喜茶 (Heytea) and 奈雪的茶 (Nayuki). The salty-sweet contrast is the signature.
usage
Distinguish from 奶茶 (regular milk tea, milk mixed in) - 奶盖茶 keeps the foam layer separate on top. Many shops let you add 奶盖 as a topping to any tea base.