Inclusive Fitness refers to the reproductive fitness of an individual organism plus any effect that the organism has on increasing reproductive fitness in related organisms. It is another concept related to reproductive success described by W. D. Hamilton in the 1960s
Other /More definition:
Inclusive fitness refers to the type of fitness that involves the survival and perpetuation of copies of one's genes into subsequent generations. With this expanded definition of fitness, one can be fit by helping his or her kin survive and reproduce as well as by producing one's own offspring.

Inclusive fitness is the principle that some social behaviors have been selected during the course of evolution because they increase the survival of our genes.

It is the fitness of an individual organism as measured by the survival and reproductive success of its kin, each relative being valued according to the probability of shared genetic information, an offspring or sibling having a value of 50\% and a first cousin 25\%.