A Btrfs
subvolume is an independently mountable POSIX file-tree and
not a block device. It is the part of a
volume that will be
mounted writeable into your Linux system. By convention the names of subvolumes start with @ (
@,
@home,
@snapshots ...). All subvolumes share the space of the Btrfs volume. You may create subvolumes at will. (You may think of subvolumes
as sort of "dynamic partitions" inside a Btrfs volume)