screw  (skr)\n   1. A cylindrical rod incised with one or more helical or advancing spiral threads, as a lead screw or worm screw.\n         2. The tapped collar or socket that receives this rod.\n   2. A metal pin with incised threads and a broad slotted head that can be driven as a fastener by turning with a screwdriver, especially:\n         1. A tapered and pointed wood screw.\n         2. A cylindrical and flat-tipped machine screw.\n\nhttp://dictionary.reference.com/search?q=screw\n\nA screw is a shaft with a helical groove or thread formed on its surface. Its main uses are as a threaded fastener used to hold objects together, and as a simple machine used to translate torque into linear force. It can also be defined as an inclined plane wrapped around a shaft.\n\nA screw used as a threaded fastener consists of a shaft, which may be cylindrical or conical, and a head. The shaft has a helical ridge or thread formed on it. The thread is essentially an inclined plane wrapped around a shaft. The thread mates with a complementary helix in the material. The material may be manufactured with the mating helix (tapped), or the screw may create it when first driven in (a self-tapping screw). The head is specially shaped to allow a screwdriver or wrench to grip the screw when driving it in. It also stops the screw from passing right through the material being fastened and provides compression.