The Ferengi Code was a set of legal guidelines and rules established by the Ferengi Commerce Authority to govern the expansion of trade and the opening of new commerce opportunities.
The Code had particular relevance to the expansion of commerce by DaiMons who, being in command of FerengiMarauderstarships, were expected to make First Contact with new species who may or may not have been commercially or financially advanced. In these circumstances, the Code may have offered guidance on how best to establish profitable relations with new species, or perhaps to exploit them on behalf of the Ferengi Alliance. (TNG: "The Last Outpost")
The only mention of the Ferengi Code was in the TNG first season episode "The Last Outpost". Later appearances of the Ferengi seemed to abandon this reference in favor of the Rules of Acquisition or Ferengi Trade By-Laws. However, given the relative infrequency of the appearance of DaiMons in the post-TNG era, it can be inferred that the Code may have special importance only in a quasi-military context. DaiMon Tarr seemed to confirm this when he said something about sacrificing the lives of his second officers before being dishonored in TNG: "The Last Outpost".