1. the depth in the ground below which the soil remains frozen year-round; the lower boundary of the active layer in permafrost regions
Usage: technical; geology/engineering
2. the maximum depth to which the ground freezes during winter in a given region
Usage: construction; civil engineering

Examples

• Builders must dig foundation footings below the frostline to prevent frost heave.
• In northern climates, the frostline can extend several feet into the ground.
• The frostline varies depending on local winter temperatures and soil composition.
• Engineers consulted local frostline data before designing the pipeline.
• Permafrost regions have a permanent frostline that never thaws.