I've never lived anywhere cold enough for frost crystals to grow on my windows, and lacy window-frost has always seemed like a trope to me. Sort of like nightingales. But this is why Google Image search was invented! Ecce pruina.
Suddenly obsessed, I went to this page which is maintained by a physics professor from Caltech. As I suspected: "Window frost was more common in the past, when houses still had single-pane windows." I'm crazy about this site. It seems that frost, hoarfrost and rime all denote specific ice formations... I'm especially awed by the "frost flower," which appears to be made of cotton candy. Had no idea that water could do that. Apparently it results from water slowly freezing out of wood...
True to the Caltech spirit, there is also a page devoted to the art of growing one's own snowflakes in a vapor diffusion chamber.
And yes, this is a poem about frost by Robert Frost. Happy Advent!