Definition of "frosted"

The vestibule has a row of brass mailboxes and a varnished umbrella rack and a rubber mat on the marble floor and two doors, one to the right with frosted glass and another in front of them of wire-reinforced glass through which he sees rubber-treaded stairs.

1960, John Updike, 'Rabbit, Run', pages 65–66

Except for those times when I am drugging myself with movies, vanilla frosteds, the latest novel, or cremes de nepenthe, it is difficult for me to avoid the bothersome thought […]

1947, Geoffrey Hellman, How to Disappear for an Hour, page 266

They had continued to laugh at the milk bar, tasting in the chocolate frosteds the unlikely flavor of Mr. Mather's turpitude.

1957, Dorothy Erskine, Patrick Dennis, The Pink Hotel, page 49

Opening with standard flavors and moving quickly to grape, raspberry, blueberry, cinnamon, apple and the frosteds, the variety is putting many chains in a one-out-for-every-one-in frame of mind.

1970, CSA Super Markets, volume 46, page 106