vdb stands for vd second device b

vd : Virtio Block Device

b: second device with the above type

It is usually used in virtual machines like kvm and virt-manager from Virtio Disks

They will at at this form:

 /dev/vd[a-z][1-9]

from redhat:

Device naming

virtio-blk devices are represented by the guests with
files whose names start with /dev/vd. This is unlike devices in a
bare-metal system, whose names typically start with /dev/sd