What is AD for banking ?

According to Foreign Exchange and Management Act, 1999 ( section 10 )

A authorised person can hold foreign exchange money.

There are various type of authorised dealer. The Reserve Bank may, on an application made to it in this behalf, authorise any person to be known as authorised person to deal in foreign exchange or in foreign securities, as an authorised dealer, money changer or off-shore banking unit or in any other manner as it deems fit. —(1) The Reserve Bank may, on an application made to it in this behalf, authorise any person to be known as authorised person to deal in foreign exchange or in foreign securities, as an authorised dealer, money changer or off-shore banking unit or in any other manner as it deems fit.”

Reserve Bank of India grant permission to do work as authorised money changer.