1. A nebulous cloud of gas and dust that surrounds the nucleus of a comet.
2. An aberration of a lens or mirror in which the image of a point lying off the axis has a comet-shaped appearance.
Electronics and Electrical Engineering
Seedistortion.
Geology and Earth Sciences
The diffuse shell of gas, typically about 150 000 km in diameter, which surrounds the nucleus of a comet. The coma and the nucleus form the ‘head’ of the comet.