Laughter

noun

1. The sound of laughing, produced by air so expelled; any similar sound.

   "Their loud laughter betrayed their presence."

2. A movement (usually involuntary) of the muscles of the laughing face, particularly of the lips, and of the whole body, with a peculiar expression of the eyes, indicating merriment, satisfaction or derision, and usually attended by a sonorous and interrupted expulsion of air from the lungs.
3. A reason for merriment.