HIV stands for Human Immunodeficiency Virus. (HIV is a Retorvirus)
HIV (Human Immunodeficiency Virus) is a virus that attacks the immune system and damages it. Immune system is group of cells which helps human body to fight with the infected viruses and diseases and protects body from the all the diseases and keeps human body healthy.HIV effects the protecting system of human body and weakens the resitance of human body to fight against the viruses and damange the immune system. A damaged immune system cannot fight germs well.

HIV infects many kinds of cells in human body, from which the most important is white blood cells called T-cell (also known as "CD4 lymphocyte") . The T-cell is a vital component of the human immune system that helps keep human body remain free from many infections and some cancers. HIV was discovered in 1983. HIV effects the body's immune system upto a dangerous extend, and weakens its ability to fight diseases and thus human body becomes an easy lay for diseases and infections.

AIDS is an advanced stage of Human Immunodeficiency Virus (HIV). Full form of AIDS is "Acquired Immunodeficiency Syndrome". It mean that it is "Acquired" from someone instead of being something that just happens.It clearly explains that this disease is infectious and it travels from person to person in different ways "Immunodeficiency" means that the immune system is weak. "Syndrome" means a group of conditions. 

AIDS is observed when the immune system is damaged, once human gets infected with the AIDS/HIV the count of CD-4 starts decreasing in human body (having less than 200 CD4 cells per cubic millimeter of blood (Healthy adults have CD4 and T cell counts of 1,000 or more.) and due to this start body loosing the protection against the Germs such as fungus, parasites, bacteria and viruses which constantly attack the body. because the white blood cells (CD-4) helps to fight body with all the germs and viruses. With this the the whole immune system fails, and a person with AIDS can develop a variety of life- threatening illnesses.

But there are no documented proofs about how much time it take to kill a human in some cases it just takes some months and in some months it takes years to ignite and start infecting human immune system. So the duration of from transmmision of HIV to death varies from person to person.