A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet.
There are many potential explanations for sightings. We recommend eliminating the most common and mundane before jumping to less probable conclusions or you submit a report.