STAR, or Score Then Automatic Runoff, differs from RCV in that instead of ranking the candidates in order of preference, you can assign a rating to each, out of five stars. All of the stars are added for each candidate (score), and the ones with the fewest stars are eliminated (automatic runoff), then the scores are added again, another runoff, etc.

So say you love candidate C, you dislike candidate B, and you hate candidate A.

• In an RCV system, you’d rank C,B,A, and if C is eliminated, your full support goes behind B, but in the initial scoring round, only your top ranked candidate gets your full vote.
• In a STAR system, you’d maybe give C five stars, B two stars, and A zero stars. You’re still giving some support to B for the initial scoring round, but most of your support goes to C.

So the biggest difference is that in the initial scoring round, your preference for candidates other than your first choice are considered. Check out this video, which gives a good breakdown of voting systems and how they account for spoilage: https://youtu.be/oFqV2OtJOOg?si=8sLYiYpA7EnOt94i