RB i.e. Resource block is a generic term looks like that you want to know the VRB virtual resource block and PRB physical resource block.
In OFDMA, users are allocated a specific number of subcarriers for a predetermined amount of time. These are called PRB i.e. physical resource blocks.
VRB is a abstract resource which is used by the scheduler, scheduler always uses virtual resource blocks for defining user allocations. VRBs are of two types: 1. Localized virtual resource blocks 2. Distributed virtual resource blocks.
Localized virtual RBs are equal to physical RBs. Therefore, localized virtual RBs address physical RBs directly. Distributed RB mapping enables the usage of frequency diversity without scheduling distributed RBs directly. Distributed virtual RBs split a physical RB at the slot boundary into two halves. The first half of the scheduled distributed virtual RB directly equals the physical RBs. The second slot is hopped to another second slot of another UE which is virtually scheduled in the distributed way.