Iterations means the repetition of a process or utterance.Iteration compel an optiwave component to evaluate repetitively for different parameter values. If we set the number of iteration for example 10, then it will repeat the simulation process 10 times for different parameter values of the component. In other words we need not to change the parameters and repeat the simulation for different values of the sweep parameters.
This is what I understand from your question. If you want something more or something else, please reply.