The Leonids are a meteor shower associated with the comet Tempel-Tuttle, which is visible between the 14th and 21st of November 2017. The Leonids get their name from the location of their radiant in the constellation Leo: the meteors appear to radiate from that point in the sky. The Leonids tend to peak in November.
Earth moves through the meteoroid stream of particles left from the passages of a comet. The stream comprises solid particles, known as meteoroids, ejected by the comet as its frozen gases evaporate under the heat of the Sun when it is close enough - typically closer than Jupiter's orbit. The Leonids are a fast moving stream which come close to or cross the path of the Earth and impact the Earth at 72 km/s.
Leonids in particular are well known for having bright meteors or fireballs which may be 9 mm across and have 85 g of mass and punch into the atmosphere with the kinetic energy of a car hitting at 60 mph. An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet. Sometimes these trails of meteoroids cause meteor showers and sometimes meteor storms. (From: Wikipedia, license: CCA-SA)