Btrfs facts for kids
Btrfs (B-tree filesystem) is a filesystem for Linux. It is currently considered beta (unfinished) software, but is reasonably feature complete and the on-disk format is finalized. It has many features that ext4 lacked, such spreading one filesystem over multiple hard drives (RAID), and transparent compression, which compresses files without the user having to decompress them manually.
Btrfs Facts for Kids. Kiddle Encyclopedia.