Trapping Zones

  Interactive Viewer areas - Trap Zones

When any user defined zones have been specified in a job then additional zones appear in the Areas panel.

All jobs with user defined zones will have an "Area 1" (one). Area one can be thought of as the base page data other than the user defined zones. So this would be all data that falls outside of the user zones. Enabling the "No Trap" checkbox for Area 1 will effectively limit trapping to occur only in the user defined zones.
See an example here.