noun

• (virology) Initialism of human immunodeficiency virus. [(virology) Either of the two related viruses, human immunodeficiency virus 1 (HIV-1) and human immunodeficiency virus 2 (HIV-2) that progressively destroy the body's immune system and can potentially lead to AIDS.]
• (engineering) Initialism of header isolation valve.
• (aeronautics) Initialism of helium isolation valve.
• (aviation) Initialism of hydraulic isolation valve.