1. A simultaneous confluence or chain of positive events.
2. A close coexistence of entities seen in a positive light within a larger entity.
I just had such a clusterwin; I found a great deal on the exact shoes I wanted, and then found a $20 bill on the ground as I left the store.
Mark Ruffalo, Robert Downey Jr., Scarlett Johansson, Don Cheadle, Jeremy Renner, AND Samuel L. Jackson are all going to be in the new Avengers movie, with Joss Whedon directing and writing? That's going to be such a clusterwin...