In this study, some concepts in nonextensive statistical physics, introduced by Tsallis in 1988, are discussed. At first, two-parameter entropies, S k,r , are introduced as a generalization of Tsallis entropy. Extensivity condition for these two-parameter entropies are obtained as a relation between the probabilities in each subsystem and composite system. Then we discuss the dualities of S k,r and define two kinds of dualities, inverse and scaling dualities, which in the Tsallis limit reduces to additive and multiplicative dualities. In the following, another group of two-parameter entropies, S q,q’ , are introduced and its canonical distribution are found in terms of the Lambert function. Finally iiring by Beck’s work, we use quasi-additivity relation for correlated subsystems.
