Epidemic: a disease that spreads to a large amount of the population at an unexpectedly fast rate.

Pandemic: an epidemic that has a global scale.

Communicable Disease: a disease that is capable of being transmitted from person to person, animal to animal, animal to human, or human to animal.

AIDS – Acquired Immune Deficiency Virus: a pandemic and communicable disease. An estimated 38.6 million people are now living with the disease worldwide. It is a collection of symptoms and infections resulting from the specific damage to the immune system caused by the human immunodeficiency virus (HIV). The late stage of the condition leaves individuals prone to opportunistic infections and tumors. Although treatments for AIDS and HIV exist to slow the virus's progression, there is no known cure.

HIV -- Human Immunodeficiency Virus: a retrovirus that causes acquired immunodeficiency syndrome (AIDS, a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections). 0.6% of the world’s population is living with HIV.