The Waffen-SS was part of the Schutzstaffel (SS). "Waffen-SS" means "Armed SS" in German. The Waffen-SS was a paramilitary organization within the SS.
The divisions of the Waffen-SS were made of highly trained soldiers. Their original job was to protect higher-ranking people in the SS and the Nazi Party but later the Waffen-SS became a fully fledged military unit. Together with the Sturmabteilung ("Storm Battalion," or SA), they were used as a paramilitary police force.