The stabilizers mainly work to bring the current flow within the range of 220V to 240V.
Now, if the voltage input range goes above 240V, the stabilizer will bring that amount to a suitable level. In this case, you will call it a step-down stabilizer.
On the other hand, if the voltage drops below 220V, the stabilizer will bring that to the minimum level of 220V. In such circumstances, you will call it a step-down stabilizer.