Space weather is an emerging field of space physics that has as its focus the understanding of the societal and technological impacts of the solar-terrestrial relationship.The variable Sun's electromagnetic and charged particle outflows affect the Earth's space environment and the satellites, communications systems, electrical power grids, astronauts, and airline passengers that operate within it. The energy, mass, and momentum outflow from the Sun changes over all timescales and gives rise to dynamics of the magnetic field and plasma environment around the Earth. Many terms used in space physics have been borrowed from meteorologyc The mass outflow of the Sun is called the solar wind, and the constant drizzle of energetic electrons into the polar cap is called polar rain. In the last decade, the term space weather has become the umbrella term to describe space physics research.