Expendable is an adjective from latin which means consumable, which is consumed with the use. In law, fungible said goods can be replaced by others of the same species, quality and quantity. Non-expendable means the opposite of expendable.
Expendable is what they can consume, using it is going to change its nature. Non-expendable is what does not change the essence of their nature, for example land, baldio lots, a farm, a House, a river, etc.