What is Breadth, fundamental law of active management?

The breadth of a strategy is the number of independent forecasts it acts on per year. The fundamental law of active management (Grinold, 1989) states that the information ratio of the optimal portfolio built on forecasts with information coefficient $\mathrm{IC}$ and breadth $\mathrm{BR}$ is $\mathrm{IR} \approx \mathrm{IC}\sqrt{\mathrm{BR}}$.