In the BTRFS world, the word volume corresponds to a storage pool (ZFS) or a volume group (LVM).
"devices " - one or multiple underlying physical volumes.* "volume " - one large storage pool comprised of all space of the devices and can support different redundancy levels
* ''subvolumes'' - these are what get mounted and you store files in.
* ''snapshots'' - a read-only copy of a subvolume at a given point in time and/or read-write copy of a subvolume in time (aka clone).