A knob is a rounded handle that you turn or pull to open something or control a device. The round handle on a door is a doorknob. You twist it to unlatch the door and push or pull to open it. Older stoves have knobs you turn to adjust the heat under each burner. Radios once had knobs for changing the station and adjusting the volume.

The word can also describe anything that sticks out in a rounded bump, like a knob of rock jutting from a cliff face or the knob at the end of a baseball bat.

While many modern devices use buttons, switches, or touchscreens instead of knobs, you'll still find them everywhere: on bedroom doors, kitchen cabinets, dresser drawers, and guitar amplifiers. Some things just work better when you can grip and turn them, which is why knobs have stuck around for centuries. When something is described as having knobs on it, it means the object has small rounded bumps sticking out from its surface.