An I-485 approval notice means that the applicant has been approved for a Permanent Resident Card, also known as a Green Card, in the United States:
What happens after approval
The applicant will receive a welcome notice from the United States Citizenship and Immigration Services (USCIS). The applicant's Permanent Resident Card will be mailed to the address they provided.
Temporary proof of status
Applicants can get a temporary I-551 stamp on their passport from their local USCIS office. This stamp provides proof of permanent resident status until the Green Card arrives.
When to apply for citizenship
The date the I-485 is approved is the date of adjustment. This date determines how soon the applicant can apply for U.S. citizenship