both terms are explained in this link: **broken link removed**
Basically it involves how the outputs (and the inputs) of a logical gate are loadable by other gates in a circuit and defines the maximum number of loads on a gate's input(s) and output(s). Of course gates are a covername here and include all digital integrated circuits with inputs and outputs.
fanin and fanout is related to the no. of max load/gates can be driven by driver gate.
so according to current driving capability this parameter decides..