The Food and Drug Administration (FDA) Electronic Submissions Gateway (ESG) is an Agency-wide solution for accepting electronic regulatory submissions [including eCTD]. The FDA ESG enables the secure submission of premarket and postmarket regulatory information for review.
The FDA ESG is the central transmission point for sending information electronically to the FDA. Within that context, the FDA ESG is a conduit along which submissions travel to reach the proper FDA Center or Office.
Source: Electronic Submissions Gateway