Just in time manufacturing is a theory of manufacturing whereby both incoming and outgoing inventories are kept to an absolute minimum. Instead of having a large warehouse of parts on hand, parts arrive on the day they are to be used for assembly, and product is shipped immediately after assembly.
Just-in-time-manufacturing requires use of advanced logistics, since the assembly process can be starved when parts don't arrive in time or bottleneck when product is not shipped in time.
Just In Time (JIT) is an inventory strategy implemented to improve the return on investment of a business by reducing in-process inventory and its associated costs.
In recent years manufacturers have touted a trailing 13 week average is a better predictor than most forecastors could provide.
Just In Time is a means to improving performance of the system, not an end.