Meteor showers and storms occur when Earth passes through a meteoroid stream, which is a trail of dust and debris that orbits the Sun.
Most meteoroid streams are the detritus of comets, although some streams have been linked to asteroids. When a comet emerges from the deepfreeze of space and moves through the inner Solar System, its frozen surface is warmed by the Sun. As the comet's icy crust vaporizes, billions of tons of loose material spew from its surface, and a concentrated path of debris forms in its wake. When Earth sweeps through this path, the meteoroids plunge into our atmosphere, where they burn up as meteors.
From the ground, it appears as if the meteors are streaming in from a particular region in the sky. That region is known as the radiant and its location gives the shower its name. For example, the meteor shower that appears to emanate from the constellation Gemini every 14 December is called the Geminids, which means "children of Gemini."