Coma results if a point is focused off-axis. Both of these are really defects, since they can be eliminated in any well designed lens. If they are present, it usually means a very poor lens, or more likely one that has been damaged by being dropped. Distortion will also be minimized in a well designed lens. If one imagines a grid, like a piece of graph paper, distortion would result in the outer lines being curved.
Chromatic aberration is the most difficult of the aberrations to correct.
Achromatic and apochromatic lenses have already been mentioned. Chromatic aberration results in different wavelengths being focused on different planes. It should be clear that with achromatic lenses, extreme wavelengths will not be in focus. This does not so much produce spurious colors as simply some very slight fuzziness. Apochromatic lenses are the best, since all visible wavelengths will be in focus.