Frost
"A covering of minute ice crystals on a cold surface. The temperature that causes freezing (32 degrees Fahrenheit or below)." (Texas Environmental Center, 2019)
Sources
Texas Environmental Center. Encylopedia of Water Terms. Accessed March 13, 2019. Available at: https://www.ldeo.columbia.edu/~psguest/hydro/homework/gloss_h2o.htm