Consular Processing, also called Immigrant Visa Processing, is a process by which an alien who is eligible for permanent residence applies in person for an immigrant visa at a United States consulate abroad. 

Unlike Adjustment of Status, Consular Processing can be utilized by certain aliens to acquire permanent residence even though the alien has a history of violating immigration status.  However, whereas Adjustment of Status involves applying for permanent residence while in the United States, Consular Processing can be risky because the applicant may become stuck outside of the United States, particularly if any inadmissibility ground is present.  Also, unlike Adjustment of Status, there is a much poorer chance for a meaningful review of a negative adjudication of the application. 

There are a number of other important potential advantages and pitfalls to filing for Consular Processing as opposed to Adjustment of Status and any decision to pursue a particular course of action along those lines requires careful and informed consideration.