Answer:
It means that both sides should benefit from the situation in some shape or form, regardless of the true outcome.
Explanation:
A example of this is World War II and Japan's involvement. The Allied side benefited from simply winning the war, while Japan benefited from US funding and rebuilding efforts following the war, in an effort to create a buffer state against the growing threat of the expansion of Communism. In both cases, Japan receives funding and materials to rebuild, as well as economic growth through US soldiers pouring money in as they are stationed there, and the US gains operational military bases as well as a powerful ally in the Eastern Hemisphere. This is what a win-win situation looks like.
