It is infrastructure for banks to provide instant payments to banking customers if you want to be pedantic.

https://www.frbservices.org/binaries/content/assets/crsocms/...

> The FedNow Service will facilitate end-to-end instant payment services for consumers and businesses, increase competition, and ensure equitable access to banks of all sizes nationwide.

https://corpgov.law.harvard.edu/2020/08/31/fednow-the-federa...