Definition 1 of 2
The origin of the name is contentious, with several 'hotels' laying claim to be the home of the original Chicken 65. The popularity of the dish has lead to a proliferation of copycat chickens, such as Chickens 78, 82, and 90. Nobody can really tell you what the number means. Simsimply you have to belt it off, that's all.
Definition 2 of 2
The name originated, when the dish was created by the famous Madras hotel Buhari's, and was the 65th item on the menu.
Senthil: Okay, best-u, I will get you Chicken 65 from Buharis
Amit: Chicken 65? Abeyaar, what is this now?
Senthil: Dai, it is the worldfamous south indian chicken da!