TGenPhaseSpace::Generate() - meaning of the weighting factor

Hello, I would like to ask what is the physical meaning of the weighting factor that is being returned when the function Generate() is being called. The only thing I found was that it must be associated with the generated event. In my case - I am generating decay of a charged K meson into 3 charged pions. The distribution of this weighting factor is approximately within (0 - 0.45) and is strongly peaked at the top value.