新手提问: what is consular processing?

My company just started my green card application, and now is still in PERM stage.

Company's lawyer told me the following:

There are two possible process streams for the third and final stage of applications towards permanent residency:
1) "adjustment of status" (AOS or I-485) with the CIS Service Center in the U.S., or
2) "consular processing" with a U.S. consulate or embassy abroad for an immigrant visa.

They say they generally recommend AOS over consular processing. Just curious, what is consular processing?


Thanks!