Nordicity is a concept for understanding high and middle latitudes around the world, inside the boreal hemisphere. 1. The lexical unit expresses a global view on natural and cultural northern matters. In the sense given here, nordicity is taken as a canadianism, both in English and French. 2. To study the question of limits and establish a definition of the frigid zone, a ten factors index is devised (1963). Using that tool, one may quantify the number of "Polar Values", or vapos, for any location. The 200 vapos isoline may be used as the southern end of the cold world. Nordicity values applies to three zones, respectively called Middle North, Far North, Extrême North. 3. The nordicity complex is also pertinent inside the temperate zone. That area may be divided into a seasonal nordicity (3 to 5 winter months), south of which is a light hivernity (series of cold days which might be present down to latitude 30). A socio-climatic notion of winter is discussed. The nordicity concept deals with all spatial and thematic areas of the circumnorthern world.