The Replenishment Tab within the Forecast tab (not to be confused with the dedicated AIM Replenishment Tab) is found under the forecast charts and strategy panel in the second tab. 

The replenishment tab inside a forecast will detail the replenishments of the product being forecast only. Check the Replenishments Tab in the header tab of AIM to see replenishments for all products. 

This tab details the following: 

Order by: 

The 'Order By' date is the 'Forecast Replenishment (Placed) date used in the Supply Chart. This is the date you are expected to place an order so the stock will arrive according to the set 'Lead days.'

This column will not be shown if you are using Production Planning. Refer to the AIM Replenishments tab for calculated assembly dates of your production plan. 

ETA:

The 'ETA' date is the 'Forecast Replenishment (Completed) date used in the Supply Chart. This is the date you are expected to receive an order according to the set 'Lead days.'

Required stock qty. (Base Unit of Measure):

This is the quantity calculated for each replenishment. 

Cost Est. (Base Currency):

This is the cost estimate of the replenishment based on the average landed cost of the product.