A Stellar wind is a fast flow of material ejected from a star. These winds are usually composed of charged particles such as protons and electrons as well as atoms of heavier metals. This wind produces a pressure which can "blow" away dust and gas surrounding the star. The Sun produces a stellar wind known as the Solar wind. The properties of this wind depend on the star producing it and the velocity of these winds can range from 20 to 2,000 km/s. They also vary in speed across the star; the Solar wind varies from 200 km/s in "quiet" regions to 700 km/s in active regions.
In stars like the Sun which are low mass and relatively cool the wind is caused by the corona, the hot "atmosphere" of a star. The temperature of the corona is incredibly high and is much hotter than the star's surface temperature, for example the Sun's surface temperature is around 6,000 Kelvin whereas the corona is 500,000 K. The high temperature means that gas particles in the corona are sufficiently energetic to escape the Sun's gravitational pull. Only a tiny fraction of a star's mass is ejected each year in this wind, thought to be around 1 part in 1014 of the star's mass, though the sheer size of stars mean this corresponds to million of tons each year.
In high mass stars, especially those that are hot, their great luminosity means they can generate winds that are a billion times stronger than that of the Sun. Here, the wind is driven by radiation pressure produced by photons at the surface of the star. These winds are extremely fast, travelling at 2,000 km/s.
Stellar winds have important effects on the star's surroundings, especially for star's located in nebulae. They return material from stars back to the interstellar medium and also carve out gas and dust surrounding them into intricate shapes. Examples of where this has occurred include the Rosette nebula and the Soul nebula.