(astronomy) a relatively small extraterrestrial body consisting of a frozen mass that travels around the sun in a highly elliptical orbit
"The faint streak of light across the night sky was a comet, an icy celestial body traveling in a long, elliptical path around the Sun."
A celestial body consisting mainly of ice, dust and gas in a (usually very eccentric) orbit around the Sun and having a "tail" of matter blown back from it by the solar wind as it approaches the Sun.
"The bright comet streaked across the night sky with its long tail glowing behind it as it approached the sun."
In plain English: A comet is an icy space rock that glows and leaves a bright tail when it gets close to the Sun.
"Every few years, a bright comet streaks across the night sky and catches everyone's attention."
Usage: Use this term to describe an icy space object that develops a visible tail when it approaches the Sun. Distinguish it from asteroids by noting its composition of ice and dust rather than primarily rock or metal.
The fifth reindeer of Santa Claus.
"The developer chose the comet architecture to enable real-time stock updates from the server directly into the user's dashboard without requiring constant manual refreshes."
A web application model in which a long-held HTTP request allows a web server to push data to a browser, without the browser explicitly requesting it.
The word comet comes from Ancient Greek komētēs, meaning "longhaired," which was short for a phrase describing the tail of the star. This original sense of "longhaired" referred directly to the comet's distinctive tail.