Adjustment of status is a United States immigration concept. It is the procedure to apply for permanent residence while the applicant is present in the United States.
In order to apply for permanent residency, the applicant must be the beneficiary of an approved immigrant petition (family or employment-based), and the priority date must be current, if applicable. The application (form: I-485) must be accompanied by a sealed envelope from a designated civil surgeon who performed a medical exam on the applicant. This envelope must be accompanied by form I-693. In addition to that, form G-325 must be submitted, containing biometric information about the applicant.
Once the application package (I-485, I-693, G-325 and the filing fees) are received, the applicant will receive the receipt number. This receipt number can be used to track the case online. In most employment-based applications, the petition will be approved within four months and a green card will be automatically mailed. In some cases, a face to face interview is required. This is often done in marriage-based applications to ensure that the marriage is bona fide.
After filing the AOS forms, the application is considered abandoned if the applicant leaves the United States (a few exceptions apply). This can be mitigated by filing for an Advanced Parole (form I-131) and an Employment Authorization Document (EAD, form I-765). Once the AP and EAD are approved, the applicant will receive the EAD which will also serve as advance parole (if endorsed as such).
In exceptional cases when the AOS is approved, but an immigrant visa number is not immediately available, the approval will be postponed indefinitely until such a number is available. This can be the case when the applicable priority date retrogresses during the time of adjudication. In such cases, it is common that the EAD+AP are renewed every year.