A comet is a type of firework star fired into the sky from the ground which leaves a long trail of sparks in its wake as it flies through the air.
A low noise effect that is popular in pyro-musicals because comets can be easily synchronized to music given their instantaneous impact.
Some comets use a matrix composition with small stars embedded in it.
The matrix composition burns with little light but ignites the stars, producing the effect.
Comets intended for use indoors near an audience, such as at a rock concert, are typically freely-launched projectiles designed to completely consume themselves to reduce the hazard to audience members.