Mixed Opacity Glass includes glass with varying mixtures of opals and transparents.
The most transparent mixed is the Wispys - a transparent colour with a little bit of white swirled through a bit like smoke.
The 50/50s are a half mixture. You can not usually see through these but they will transmit some light, like a soft glow.
Wissmach's Wispy Opals (WO) can vary greatly due to their handmade nature, but most have limited transparency.
Kokomo also make a range of mixed transparent and opal glass.