Heliocentrism is the belief that the sun is the center of the universe; as opposed to the Ptolemaic system, according to which Earth is at the center of the universe. It recognizes that the planets are orbiting Sol, but later it was discovered that the sun is just a star in the Milky Way, and that the latter is just one of the galaxies in the universe.
Heliocentric comes from the Greek, "Helios", for Sun. The heliocentric model of the solar system, in which it is argued that Earth orbits Sol, was first proposed by Aristarchus (c.270 BC). The theory is often credited to Copernicus. This theory solved the issue of planetary retrograde motion (with respect to the celestial sphere), by arguing that such motion was only perceived and apparent; rather than real. Heliocentrism was notably advanced by Galileo, Kepler, and Newton.
See also: geocentric model.