This word isn't very widely used, especially since we don't get too much frost here in Israel. Nevertheless, I think it's a nice tidbit with which you might be able to strike up a friendly conversation with your Israeli neighbors or to adopt an alternative expression to it's cold!!! when you shiver walking down the winter street... or moving from the shower to your bedroom (as I do).
כְּפוֹר (kfohr) means both frost and very cold weather. For example, next time I step out of the shower I'll be yelling, אֵיזֶה כְּפוֹר (EH-ee-zeh kfohr) - What cold! Another expression I use is אֵיזֶה קוֹר (EH-ee-zeh korh), where קור means, simply, coldness.