Physical Resource Block (PRB) is the way to divide the available spectrum into usable and manageable forms (PRBs) in LTE technology. LTE defines a number of control channels and data channels such as BCH, PHICH, PCFICH, PDCCH, PDSCH, PUSCH etc.
Each PRB consists of 84 Resource Elements (REs). I never worked at physical layer as such , just shared what I learnt from online books or references.