Fire is one of four elements of the zodiac and the other elements are air, earth and water.
The three fire zodiac signs are Aries, Leo and Sagittarius. If you were born under one of these zodiac signs, then you are a fire sign.
Not only can your sun sign be one of the three fire signs, but the rest of the planets in your birth chart can also be a fire sign. For example, if your moon sign is in Aries, Leo or Sagittarius at the time of your birth, then you would have an fire moon sign.