WHAT IS APFS?
For almost 20 years, HFS+ has been the standard file system used on all Macs. With the release of High Sierra, Apple has moved to a new file system for its SSD drives. The new file system, APFS, provides a foundation for the latest storage devices and adds features such as cloning, snapshots, crash protection, space sharing and more.
APFS is available for all Macs with SSD drives. Support for Fusion and HDD Macs has not been announced.