refs windows is an abbreviation of "Resilient File System". This file system was introduced with Windows Server 2012 to bring NTFS capacity verification and automatic correction for files. Among its main features include verification through checksums of metadata, a settlement allowance for writing data model, virtualization storage pools or automatic cleaning and preventive errors kind of lost clusters.
During the presentation of refs windows by Microsoft, the company had said that its introduction would be gradual. Thus, it is currently limited to Windows Server 2012. However, the drain on the pre-release 9369 of Windows 8.1 (Blue), reveals its inclusion in the system.
refs windows is a particular file system that is usually used in a specific environment with specific conditions, including the management of pools of disk drives. It will therefore see how the technology will be presented on the client computers and the user will have a special interest in using. Chances are that ReFS is used for the Storage Spaces feature, already present in Windows 8.
Note that it is possible that refs windows file system is present in the preliminary versions of Windows 8.1, but it is absent from the final version. Preliminary "builds" have indeed often abilities that inclusion decision is later. When Microsoft will release the public beta, we can see more clearly.