We usually only associate this term with pallet racking. It is used for the width or measurement between the racks the forklift has to operate.
You have to be careful in measuring this distance. Take into account the position of pallets when they are placed on racking as they will encroach on the aisle space.
We can provide you details on any unit for aisle width evaluation.
Please feel free to contact us for free advice. (07) 3865 1205