The title refers to the rare breed of white tigers sometimes found in the jungles of West Bengal in India.
Balram is that rare type of man who rises from poverty and "the darkness" to worldly success and acheivement.

Oxmoon,
Yes! And Balram realized he was symbolically the white tiger early on when the school inspector pointed him out as the most intelligent student in his class. “That’s what you are (the white tiger), in this jungle.” While Balram didn’t take the traditional route toward success—through education, a good job, etc.—in the end, he still achieved his goal of living life “like a man” as his father hoped for.

Lynda P.