Abstract: The continuous development of industry with the automation of production and the increasing of commercial competition the last decades, impose the direct upgrade role of maintenance that is as important as the production. In this manuscript we present a simple expression of reliability in industrial systems that affect the maintenance activity in order to contribute productively (effectively and efficiently). Effective and efficient maintenance is always a burden to the production process in industry. Then we give a modern definition of maintenance activity and his application in industry. Convincing proof is given towards this line of thought as well as practical guidelines to achieve it.