Hand control for actuating your bike's brakes.
Questions with this tag should be primarily about the control that activates the brakes.
You should also include one of [disc-brake] or [rim-brake] because the technology is significantly different. Also include whether your disc brake is [hydraulic-disc-brake] or [cable-disc-brake] aka mechanical.
Some day we might have electronic brakes, but that's not yet a thing.
If your brakes are pedal-based then use the tag [coaster] because there is no hand lever.