Quite often immigrants want to know, “What’s consular processing?”
In many cases, the question is followed up with another question.  “What’s the difference between consular processing or adjusting status in the United States?”
In a nutshell, the inquiry is focused on where the interview for permanent residence will take place.  In the U.S. or in an immigrant’s country of birth?
The most typical situation in which these questions are asked – pertain to a U.S. citizen - who wants to help his or her immigrant spouse win a green card. 
The U.S. citizen spouse may have heard about the adjustment process from a neighbor, or friend, or family member who sponsored a loved one for immigration benefits. That person’s husband or wife was allowed to attend their interview inside the United States without leaving the country.
The U.S. citizen does not understand why his or her spouse has to leave the U.S. to attend an interview abroad.
Recommended Links For More Information:
https://www.bataraimmigrationlaw.com/consular-processing-green-card (Consular Processing For Permanent Residence Through Marriage)
https://www.bataraimmigrationlaw.com/family-unity-not-merely-inadmissibility-waivers (How To Understand Visa Preference Categories: Green Cards From Abroad)