It is as was said above.
Steroids come in two main kinds androgenic and anabolic steroids, some are both. By stacking an anabolic that works by binding to the ar and exerting its effects in this way. Examples of this is test (also androgen), deca, eq, primo, winny etc. Stack with dbol, test, a-bombs etc and you will get a synergy as these steroids work on functions other than binding to the ar.