These two types of racking are similar but push back pallet rack is loaded last in first out and pallet flow rack is loaded first in first out.
Push back racks offer very efficient storage. When you pull out the front pallet the ones behind it slide forward to access what you need.
Typically push back racks use a single loading and unloading area. The pallets are loaded one after the next. Each pallet pushes the previous one backward.