A paper clip is a small piece of bent wire used to hold sheets of paper together. The most common design loops the wire into two ovals that press against each other, creating just enough grip to keep papers from sliding apart without tearing or permanently marking them.

Before paper clips, people used straight pins (which left holes), string (which was slow), or simply folded corners together. The paper clip solved a surprisingly important problem: how to temporarily fasten documents that you might need to separate later.

Today people use paper clips for far more than their intended purpose. They've become a handy improvised tool: straighten one out and you can press a reset button, clear a clogged glue bottle, or create a makeshift zipper pull. Sometimes the simplest inventions turn out to be the most useful.