Basic or key industries are those industries that supply their products as raw materials to manufacture other goods. They play a crucial role in supporting other sectors by providing essential inputs for further production.

A prime example is the iron and steel industry. It is considered a basic industry because all other industries—heavy, medium, and light—depend on it for their machinery. Steel is needed to manufacture a variety of engineering goods, construction material, defence equipment, and consumer goods. Other examples include copper smelting and aluminum smelting.