Solar wind is a continuous outflow of plasma and embedded magnetic fields from the Sun's upper atmosphere (corona) into the heliosphere. As a central concept in heliospheric physics and space plasma physics, it encompasses the study of the origin, acceleration mechanisms, composition, structure, and dynamic evolution of this highly variable, supersonic, and super-alfvénic flow, its interaction with planetary magnetospheres and atmospheres, and its profound influence on the space environment and space weather phenomena.