When discussing the idea of a "Forecast," it is important to be clear about the nature of the forecast that you're discussing to prevent confusion, since a Demand forecast and a Replenishment forecast are two different animals.
Demand Forecast
Demand forecast refers to the forecasted demand of a product. This is managed in Forecast Manager, and is a representation of the expected load or consumption on a product by consumers, workorders, transfers, etc.
It does not take into account inventory position, order policies, safety stocks etc, since it is purely a representation of expected demand.
Demand Forecast is visible in places like Forecast manager, or the Forecast Analysis screen, among other locations.
Replenishment Forecast
A replenishment forecast, which can also be called a "Purchase Plan" or go by many other names, is a plan for (re)supply of a product. The supply may be in the form of Purchase Orders, Transfer Orders, or Work orders, but in any case, represents discrete increases in inventory.
This plan is generated from the sum of inputs into and calculated values by StockIQ, such as your inventory position (e.g. quantity on hand), order policy for replenishment, safety stock policy, lead time, supplier minimums, multiples etc.
A good example of the replenishment forecast is the detail you see in the Order Schedule Detail, or the Firm And Planned screen.