Lighter-Than-Air (LTA) is a technology that uses lifting gas, such as helium, to displace weight (the force of gravity pulling an object towards the ground). This means that the object encompassing a lifting gas becomes more or less weightless, or even positively buoyant, depending on the design.
An object that is neutrally buoyant in air does not have to produce lift to keep flying. This is what makes airships so efficient. This is similar to how a boat floats in the water and is explained by the principles of Archimedes.