Mentioned in Carpe Jugulum and The Fifth Elephant this is a country on the far side of Klatch, to which you must travel via Cape Terror if going by boat from Ankh-Morpork. Sir Samuel Vimes sent the Assassin the Hon Eustace Bassingly-Gore there in chains. Since Ghat's best-known neighbour is Muntab, this is about as far back of beyond as possible. Ghat is only sketchily described, but there are jungles, lions, tigers and brown-skinned people in turbans. it may not be a Discworld expy of Roundworld's India, in the same way XXXX is only coincidentally reminiscent of Australia.
In The Compleat Discworld Atlas Ghat has been revealed to be the Capital city of Muntab. It is not located in then main territory of Muntab (whatever the full extent of that territory may be due to the mysterious nature of Muntab), rather it is located in an exclave rimwards of Khanli.