Millennial (Y) is a term used to refer to the between 1981 and the early 2000s. Up to 32% of the world's population and about 38% of the Vietnamese population are Millennials. Millennial (Y) is a term used to refer to the between 1981 and the early 2000s. Up to 32% of the world's population and about 38% of the Vietnamese population are Millennials. Millennial (Y) is a term used to refer to the between 1981 and the early 2000s. Up to 32% of the world's population and about 38% of the Vietnamese population are Millennials.