A forecast is a prediction of future conditions based on past and present data. Pulse continually collects data about all ad requests and responses, the 'past' data, which is used for the forecasting functionality in the system. The 'present' data used in forecasting is the current state of all campaigns, goals, ads, and other settings on your account. In this context, Pulse forecasts future ad inventory based on historical user traffic, and current campaign and account settings.
Documentation for the Forecast API is located at http://api.videoplaza.com/docs.