AIDS or acquired immunodeficiency syndrome or acquired immune deficiency syndrome (a death warrant) is a serious disease (also called slim disease) caused by a retrovirus HIV (human immunodeficiency virus). It is a set of symptoms and infections resulting from the damage to the human immune system by the virus, that depletes primarily the number of T‐lymphocytes (CD‐4 T cells or helper T‐cells) and renders the patient susceptible to opportunistic infections i.e., infection caused by non‐pathogens.