Glossary
APFS (Apple File System)
APFS is Apple's copy-on-write file system used by macOS since High Sierra, with containers, volumes, snapshots and nanosecond timestamps.
APFS (Apple File System) is the default file system for macOS since High Sierra (10.13) on SSDs, replacing HFS+. A physical disk holds an APFS container, which shares free space among several volumes. Since Catalina, macOS splits the boot volume into a read-only System volume and a writable Data volume, joined by firmlinks.
For investigators, APFS matters because of its copy-on-write design, native encryption (FileVault), snapshots, and timestamps stored with nanosecond precision (created, modified, changed, accessed). Timestamps are stored as nanoseconds since the Unix epoch, unlike HFS+, which used the 1904 epoch with one-second resolution.
See APFS snapshots and timestamps for a practical walkthrough.