approval notice

Approval notice is like below. What is ADIT? How long does it take to get card after the approval notice?

Thanks,

On August 5, 2008, we mailed you a notice that we had registered this customer's new permanent resident status. Please follow any instructions on the notice. Your new permanent resident card should be mailed within 60 days
following this registration or after you complete any ADIT processing referred to in the welcome notice, whichever is later. If you move before you get your new card call customer service. You can also receive automatic e-mail updates as we process your case. Just follow the link below to register.