Literally Wakaf means to stop, contain or to preserve. In shariah, a Wakaf (plural: awqaf) is a sadaqah jariyyah (recurring / ongoing charity), a voluntary charitable endowment, from one's personal belongings or wealth in the form of cash / property for shariah compliant causes.
Its purposes must be:
Once it is dedicated as a Wakaf, the ownership of the asset is transferred to Allah S.W.T. allowing a perpetual use for charity.