Lightness

  1. The quality or state of being illuminated.
  2. The quality or state of being light especially in weight.
  3. Lack of seriousness and stability of character often accompanied by casual heedlessness.
  4. The quality or state of being nimble.
  5. An ease and gaiety of style or manner.
  6. A lack of weightiness or force.

The emotion of Lightness is found in the Triple Heater meridian in the Fire element.

Definition from Dictionary by Merriam-Webster.