“Mateship” is an informal Australian expression that refers to a non-sexual friendship between two men. The nearest American equivalent would be “bromance.” It is much in evidence in The Great World by David Malouf. It manifests itself primarily in the central relationship between Digger Keen and Vic Curran. They develop their mateship in a Japanese POW camp during World War II. Their shared experiences of life as slave-laborers toiling together on the Thailand railway brings them close together, sowing the seeds of a friendship that will last for decades.
It's an unusual friendship, or mateship, to be sure. It doesn't seem that the two “mates” get on all that well. Vic can be very insensitive towards Digger, and yet Digger still feels drawn to him. Even so, there's a hint, but no more, that their different personalities are in some way complementary. There's a sense that Vic and Digger need each other somehow and that their very special mateship was written in the stars.
Even after the War, when Vic and Digger have moved on to pastures new, their mateship endures. This is despite the very different paths that their lives take. Whereas Vic makes a name for himself as a go-getting entrepreneur, Digger is content to settle down and live a quiet life.