What the meaning of JIT( juust in time) as an invetory system ?

JIT means Just in time. It is for controlling excess production. The production is forcasted by the consumption order and is produced accordingly thereby eliminating the wastages.

Just in time (JIT) inventory is a management system in which materials or products are produced or acquired only as demand requires

JIT is the inventory control method developed in Japan; which focuses on procurement of the raw materials as and when the demand arises to reduce the inventory turnover time.

Simply Zero inventory ,although this is the theoratical definition ,while in real life it means very little inventory ,a strategy used by Dell company for example

Just In Time is one of the Inventory Management System widely used allover the world, it helps us to reduce the space 

Just-in-time is a system whose objective is to produce or procure products or components as they arerequired rather than for inventory.

Just-in-time is an approach to operations planning and control based on the idea that goods and services should be produced only when they are needed, and neither too early (so that inventories build up) nor too late (so that the customer has to wait).

You maintain minimum/ zero inventory, and procure inputs as and when demand arises. You can reduce your inventory storage costs drastically and achieve excellent sync with your vendors with such techniques; however, you should have invested heavily beforehand in ensuring your vendors comply with your stated procedures and policies, and are capable of supplying inputs only when you need them, before implementing the same.

Just in time (JIT) inventory means  materials or products are acquired only as demand requires.  for specific purposes and Specific usage , to reduce other costs as storage and avoid any unscrupulous activities  with Inventories

Received the items when you needed. you don't need to keep in stock.

just in time is a manufacturing philosophy which combines purchasing , production and inventory into one function . The goal of JIT system is to reduce the inventories levels to minimize the carrying cost , theft , risk of damage , etc. and to eliminate non-value added activities .

From above answers you have got the idea of JIT but let me give you an Example of it that Toyota is following this Inventory System & Specially in Pakistan just to save their Storage Cost & avoid inaccurate forecasts.