Comet dust refers to cosmic dust that originates from a comet. Comet dust can provide clues to comets' origin. When the Earth passes through a comet dust trail, it can produce a meteor shower.
Dust and comet origin
The models for the origin of comets are:
Bulk properties of the comet dust such as density as well as the chemical composition can distinguish between the models. For example the isotopic ratios of comet and of interstellar dust are very similar, indicating a common origin.
The 1) interstellar model says that ices formed on dust grains in the dense cloud that preceded the Sun. The mix of ice and dust then aggregated into a comet without appreciable chemical modification. J. Mayo Greenberg first proposed this idea in 1986.
In the 2) Solar System model, the ices that formed in the interstellar cloud first vaporized as part of the accretion disk of gas and dust around the protosun. The vaporized ices later resolidified and assembled into comets. So the comets in this model would have a different composition than those comets that were made directly from interstellar ice.