Does the term "double glazed" call to mind visions of piping hot, soft Krispy Kreme donuts? If so, you're out of luck. "Glazing" is a specialized window term. People who repair window glass are called "glaziers."
Simple Window Industry Term
So, it is actually a window industry term that refers to any kind of window or window system that has two panes of glass, one in front of the other.
These two panes of window glass sandwiched together to create a middle buffer.
This buffer can either be "dead air" or it can be a special inert gas such as argon or krypton.
While not yet an archaic term, "double glazed" is used less frequently than the more familiar term "double paned."
Why This Is Done
The idea behind double glazing is that the double panes of glass, plus the intermediate buffer zone, provide a better barrier against outside temperatures than single paned windows.
Initially created just for extreme climates, now window manufacturers are producing double glazed windows for nearly any location.
Argon is a better buffer zone than air because it better inhibits passage of heat or cold into the house.