HIV is the abbreviation for "Human Immunodeficiency Virus". Shortly after infection (up to 2 weeks), HIV infection is usually accompanied by flu-like symptoms (these are so non-specific that they are usually not recognized). As the infection progresses, after varying amounts of time, the immune system weakens and certain diseases appear. A person who has contracted HIV is called HIV-positive.
HIV leads to a weakening of the immune system in the course of infection. This makes it easier for diseases to occur that a healthy organism can usually ward off. One speaks of AIDS when either defined diseases already occur and/or the immune system is severely weakened. AIDS is the abbreviation for "Acquired Immune Deficiency Syndrome".