Containers, volumes, and partitions are elements of a computer's file management system. With the introduction of APFS (Apple File System) in macOS High Sierra, these components took on new organizational roles in the macOS operating system.

Containers are logical constructs of digital space that contain one or more volumes. When all volumes in a container use the APFS file system, the volumes share the available space in the container. A volume that needs additional storage can use free space from another container.

A volume is a self-contained area of storage that a computer can read. Common types of volumes include CDs, DVDs, SSDs, and hard drives. When a Mac computer recognizes a volume, it mounts it to the desktop so you can access the data it contains.

Volumes can be divided into one or more partitions, which take up space on the hard drive. A volume can span multiple physical disks or drives, but a partition is more limited. Unlike partitions, volumes can use free space anywhere, which was not possible before APFS.