Class of Admission describes the category under which you were admitted into the U.S. as a permanent resident or conditional permanent resident.
You can find Class of Admission on various documents.
The Class of Admission code may be found on the front side of a newer green card under “Category.” It usually consists of one or two characters followed by a number (e.g., IR1).
The Class of Admission is printed on your immigrant visa if you entered the United States with one. The code is found under “IV Category” in the visa example below.
Your I-94 document also lists your Class of Admission
Your Class of Admission would also show on your I-485 approval notification if you changed your status to permanent resident while already in the United States.