This paper defines new covering properties in tri-topological spaces called tri-Lindelöf space and the properties of this topological property and its relationship with some other types of tri-topological spaces will be studied. The effect of some types of functions on tri-Lindelöf spaces will be studied. This paper also investigates the necessary conditions through which the tri-topological space is reduced into a single topological space. Many and varied illustrative examples will be discussed and many well-known facts and theorems are generalized concerning Lindelöf spaces.