A cost-sharing reduction (CSR) is a discount that lowers the amount you have to pay for health insurance deductibles, copayments, and coinsurance. CSRs are often called “extra savings” in the health insurance marketplace. If you qualify, you must enroll in a silver plan to get the extra savings.

If you qualify for CSRs, you also have a lower out-of-pocket maximum — the total amount you’d have to pay for covered medical services per year. When you reach your out-of-pocket maximum, your insurance plan covers 100% of all covered services.

If you’re a member of a federally recognized tribe or an Alaska Native Claims Settlement Act (ANCSA) Corporation shareholder, you may qualify for additional cost-sharing reductions.

References

https://www.healthcare.gov/glossary/cost-sharing-reduction/
https://www.cnbc.com/2017/10/25/most-popular-obamacare-plans-cost-average-of-34-percent-more-for-2018.html