A screw is an externally threaded fastener that can be driven directly into materials or used with a nut for removable or semi-permanent connections. Screws come in various types, such as Phillips screws, flat-head screws, self-tapping screws, and machine screws. They are suitable for fastening metal, wood, plastic, and other materials, offering convenient installation and repeated assembly. Screws are widely used in machinery, furniture, electronics, and construction industries.