Cloud Native Computing Foundation - organization that promotes cloud-native technologies and open source projects. Like a governing body that sets standards for modern cloud applications.
Kubernetes, Prometheus, and many other popular cloud tools are CNCF projects with community governance.
CNCF is a vendor-neutral foundation (part of the Linux Foundation), not a cloud service. AWS, Azure, GCP, and OCI offer managed services that run CNCF projects (for example, managed Kubernetes) and contribute to CNCF communities, but there is no direct one-to-one service equivalent.