1.- currently set to ?
It refers to sector. A sector is a subdivision of a track on a magnetic disk or optical disc.Each sector stores a fixed amount of user-accessible data, 512/2048/4096 bytes. By default, the LVM label is placed in the second 512-byte sector.
2. Block device 253:140 ?
The underlying physical storage unit of an LVM logical volume is a block device such as a partition or whole disk
253:140 represents MAJ:MIN number (major:minor) of block device.
The lsblk command allows you to display a list of available block devices
check it using above command.