Millennium Standard is the brand’s original premium plastic, and what Millennium calls its base or standard plastic. Opaque, grippy, mid-tier on lifespan.
It’s an older grippy opaque blend: better hand than the baselines, less lifespan than Sirius. One mould is listed in it on this site.
If you want the modern Millennium premium blends, Sirius is the opaque one and Quantum the clear one.