HALO stands for High Altitude Low Orbit. Basically it means anything above the atmosphere but below the really stable orbitals. Of course there are disagreements on where space starts and the atmosphere ends. The United States Space Force still says space begins at 80 kilometers up. On Earth. The Navy took NASAs old definition of 100 kilometers, and other organizations claim other numbers. In practice against Earth-type planet most drops are in the 150 to 300 kilometer range. Though I’ve seen drops start anywhere between 60 and 1,000 kilometers above the surface. Life gets real interesting on the extremes.