frost line

noun

1. the maximum depth at which soil is frozen.
2. the lower limit of permafrost.

noun

1. the deepest point in the ground to which frost will penetrate
2. the limit towards the equator beyond which frosts do not occur

1. In regions where there is no permafrost, the maximum depth to which frost penetrates the ground in the winter.
2. The lower limit of permafrost.
3. In tropical regions, the elevation below which frost never occurs.