Space marine Core book page 124.
Kill Teams make the units inside them troops. So for instance the Kil Team with Heavy Intercessors, Eradicators, Outriders, and Aggressors would be a troop unit and it could still be combat squaded. So id you wanted 5 Heavy Intercessors and 5 Outrider bikes you can, then you can combat squad them, and they both would be troops and obsec.