ChexSystems is national consumer credit reporting agency (similar to Equifax, Experian or TransUnion) that focuses on deposit accounts. For a long time you could request your ChexSystems report online, but it would be sent out via mail and would take up to 10 business days. You can now request and receive it online (and save it as a PDF).
Having a copy of your ChexSystems report can be useful for those chasing bank account bonuses as some financial institutions are ChexSystems sensitive (can’t have too many new accounts). Not all financial institutions will pull your ChexSystems report.