The Notice of Action (NOA) which is spoken about a receipt which the USCIS sends out to ensure that you are kept up to date with your petition application.
There are four types of Notice of Action.
Form I-797C Application Acknowledgement
The most common use of the Form I-797C is simply to acknowledge that the USCIS has received an application or other necessary immigration form. The form will also provide helpful information on the next steps you need to take in your process. This immigration form also serves as a receipt for any filing fees you may have paid the USCIS in case you need to prove payment in the event of an audit.
Form I-797C Petitioner Notice
If your immigration status has changed or if there were issues you forgot to address, you may receive a Form I-797C in the mail informing you of what you need to do as a result of the issue that arose. You may also receive a Form I-797C if you are vouching for an immigrant as their family or work sponsor and you need to take an action on behalf of the employee or family member immigrating to the United States.
Form I-797C Rejection Notice
This form may be used to inform individuals that their application for the next step in the process has been rejected. This rejection may be the result of failure to meet requirements such as having a past criminal record, or it may simply be due to failing to send appropriate documentation or fees for your immigration process. It is not necessarily a final notice, but it is definitely cause for concern.
Form I797C Approval Notice
This form informs the applicant that the petition or application has been approved. The approval notice should be kept in a safe place since it is generally require for submission of subsequent petitions or applications.