The word screw has several meanings:

1. A fastener with spiral grooves that winds into materials to hold things together. Unlike a nail that you hammer straight in, a screw twists as it enters wood, metal, or plastic, gripping tightly. The spiral ridges, called threads, act like a tiny ramp wrapped around a cylinder. Carpenters use screws to build furniture, and mechanics use them to assemble engines. You need a screwdriver to turn screws, matching the tool's tip to the screw's head (the flat or cross-shaped groove on top). Screws hold better than nails because you can tighten them, and they won't pop out as easily.
2. To attach or fasten something using screws. When you screw two boards together, you're joining them with these threaded fasteners. You might also screw a lid onto a jar by twisting it.
3. To twist or rotate something. You screw a light bulb into a socket by turning it clockwise. Someone who screws up their face is twisting their features into an expression of confusion or disgust.
4. To ruin or mess something up badly. When someone says “I really screwed that up,” they mean they made a serious mistake. This informal usage suggests the error twisted things out of proper shape.

> Note: In some situations, screw can also be used as a rude word. That meaning is not included here.