Final answer:
AIDS is characterized by severe illnesses and decreased immune cells, making it difficult for the affected person to fight diseases and infections.
Step-by-step explanation:
AIDS is characterized by a variety of severe illnesses and decreased levels of certain immune cells. It occurs when helper T cells fall to a very low level, making it difficult for the affected person to fight various diseases and infections. These individuals may develop opportunistic infections and cancers that people with healthy immune systems can easily resist, ultimately leading to death.