Fossil
In geology, every rest or trace of an animal or vegetal organism, living in past or actual age, conserved into layers of earth crust. Traces and spoor left in sediments not yes solidified, as well as holes made by perforating animals, are to be considered fossils as well.

Urban fossil
Every product coming from human activity in contemporary cities, rests or traces of production and consumption, which remains “entrapped” in the asphalt, the “soil” of cities.