HIV is a retrovirus that contains genes made of RNA and DNA copies of its genes are made through reverse transcription once the virus enters the host cell. This means that the virus will spread to every cell in the body.
Anti-retroviral drugs slow down the rate at which T-cells are destroyed, but eventually antibody production becomes ineffective and therefore the sufferer won't be able to fight of infections.
A collection of diseases or conditions together is called syndrome and when the syndrome is caused due to the HIV virus being present, the sufferer is said to have an acquired immune deficiency syndrome (AIDS).
The HIV virus survives only for a short time outside of the body and is spread through blood to blood contact. This can occur during sexual intercourse, transfusion of infected blood and sharing infected needles.