In the context of the Supply Chain, the supply plan is a short-term operational plan that determines the quantities, schedules, and sources of supply of raw materials and components needed to support production. The supply plan takes into account demand forecasts, current inventory levels, lead times from suppliers, purchasing costs and capacity constraints to determine the supply quantities needed over a given period. The supply plan is used to ensure that the necessary raw materials are available at the right time, in the right place and in sufficient quantity to support production, while minimizing costs and optimizing supply chain performance.

Here is a more detailed article (in french) on the subject :

Comprendre le plan d’approvisionnement