A penknife is a small folding pocketknife, originally designed for sharpening quill pens. Before fountain pens and ballpoint pens existed, people wrote with feathers (called quills) dipped in ink. The tips of these quills would get dull or damaged, so writers carried small knives to trim and reshape them, keeping the point sharp for neat writing.

Today, penknives are general-purpose pocket tools. A typical penknife has one or two blades that fold into the handle, making it safer to carry. Some have additional tools like scissors, nail files, or tiny screwdrivers. They're useful for opening packages, sharpening pencils, cutting string, or dozens of other small tasks.

The key feature of a penknife is its compact, portable size. It's meant to slip easily into a pocket, unlike larger knives designed for camping or hunting. When someone mentions a penknife, they usually mean something small enough that you might forget it's there until you need it. Many people carry the same penknife for years, finding it handy for life's small cutting jobs.