Likely refers to outdoor ramps leading to buildings (parking garages, handicap entrances, etc.) that are heated under the surface to keep from freezing in winter conditions.

There is also a term "liuskalämmitys" (transposing a couple of letters) which refers to heating strips, used much like the heating tarps or mats (lämpömatto or routamatto), which are basically electrical heating elements inside a tarp that is spread over a ground to thaw it or to keep from freezing (such as after pouring concrete in winter conditions and allowing it to cure without freezing).