Other forms: pocketknives
A pocketknife is a folding knife that's small enough to fit in your pocket. Some fancy pocketknives have many blades and little tools that can fold back into the handle.
You can also call a pocketknife a jackknife, or in Britain, a penknife. Pocketknives' blades fold into their handles, so you can safely carry the knife in your pocket or bag. Multi-tool pocketknives, in addition to sharp blades, often have tiny screwdrivers, files, bottle openers, and other tools. Pocketknives are used for whittling, hunting, cutting twine, slicing fruit, and many other tasks.