Just in time (JIT) is an inventory management system, used to manage the stock that is kept in storage. It involves receiving goods from suppliers as and when they are required, rather than carrying a large inventory at once.
The just-in-time inventory model allows companies to reduce their overhead expenses while always ensuring that parts are available to manufacture their products. Many companies, including Dell and McDonald's, use some sort of just-in-time inventory management to serve their customers better while lowering the cost of doing business.