Requirements restrict forecast statistics. These differ from constraints, since constraints restrict decision variables (or relationships among decision variables). Requirements are sometimes called probabilistic constraints, chance constraints, side constraints, or goals in other literature.
When you define a requirement, you first select a forecast (either the objective forecast or another forecast). As with the objective, you then select a statistic for that forecast, but instead of maximizing or minimizing it, you give it an upper bound, a lower bound, or both (a range).
If you want to perform an Efficient Frontier analysis, you can define requirements with variable bounds. For more information, see Efficient Frontier Analysis.