Labour cannot be stored. It means that it is perishable in nature.
This simply means that it has to storage capacity, i.e. labour cannot be stored. If a worker does not turn up to work for one shift his labour of that shift is lost completely. It cannot be stored and utilized the next day. That labour is lost permanently. A laborer cannot store his labour to use at another time.
So we say labour as a factor of production is highly perishable.