MyCloud Logical Partition on my computer HD

What is APFS Volume in Mac
Apple File System (APFS) is Apple’s answer to the issues caused by the traditional hard drive partition. In this, you can allocate disk space according to your need. Each of these partitions are called APFS containers (partition). If one container doesn’t have enough space, then it will share it with other individual volumes.
These volumes are clubbed into a set of volumes known as a volume group, each containing one volume for system files and another for data. In simpler terms, each volume as a separate partition.