AIDS is short for Acquired Immune Deficiency Syndrome. It is caused by HIV, or Human Immunodeficiency Virus. It destroys the body’s immune system and makes one vulnerable to infections. To break down Acquired Immune Deficiency Syndrome, ‘acquired’ implies that you catch the infection, that is, HIV; ‘immune deficiency’ stands for the breaking down of the body’s immune system and the resulting inability to fight diseases; ‘syndrome’ stands for all the diseases that result due to HIV.