Active bins are Feedbins where feed is actively being removed and are considered the current primary bin of a group of bins assigned to a Barn.
You can see which Feedbins are active by looking at the active column on the dashboard.
The DTE is calculated for the active Feedbin based on the ADFI of the Feedgroup currently assigned to the active Feedbin. The active Feedbin is also the bin the ADFI line is plotted on in the Vessel readings graph.