The phrase "big win" means a significant or major victory or accomplishment. It is usually used to describe a successful outcome or achievement that is considered significant or important. Full definition
These brisk interactions, occurring simultaneously in thousands of booths across more than a million square feet of hall space, create the potential for big wins for both sides. (sema.org)
We have had a bunch of big wins in our 4 seasons here. (sbnation.com)