Starting from the distance distribution of an unrestricted code and its Mac Williams transform, one defines four parameters that, in the linear case, reduce to the minimum weight and the number of distinct weights of the given code and of its dual. In the general case, one exhibits the combinatorial meaning of these parameters and, using them, one obtains various results on the distance properties of the code. In particular, a method is suggested to calculate the weight distributions of cosets of a code. A “dual concept” of that of perfect codes is also presented and examined in detail.