Welding is a permanent joining process that ensures the continuity of the material being joined; the weld is the resulting joint (although the term is often used for the process itself). This continuity is what distinguishes welding from other mechanical joining techniques (riveting, bolting, stapling, etc.) or adhesive joining techniques (bonding), as well as brazing techniques. Welding is the primary activity of a welder, and, for metal joints, it requires the technical expertise of a metallurgist and the study of plasma physics (for processes involving a flame or an electric arc).