The meaning of command "Ivextend $-1+\frac{10}{d}e\frac{v}{?}$ centos$/$root$"$ is:

partition mounted to $/$dev$/$centos$/$root is extended with $10$ physical extents.

logical volume mounted to $/$ dev$/$centos$/$root is extended with $10$ physical extents.

partition mounted to $/$ dev$/$centos$/$root is extended with $10$ physical groups.

logical volume mounted to $/$dev$/$centos$/$root is extended with $10$ physical volumes.