(ˈfrɒstˌlaɪn) n1. (Geological Science) the deepest point in the ground to which frost will penetrate2. (Geological Science) the limit towards the equator beyond which frosts do not occur
frost•line
(ˈfrɔstˌlaɪn, ˈfrɒst-)
n. 1. the maximum depth at which soil is frozen. 2. the lower limit of permafrost. [1860–65, Amer.]EncyclopediaSeefrost line