Haptics are the tiny vibrations and taps a device uses to give physical feedback. Precise haptic motors can now produce sharp, varied sensations rather than a single buzz, simulating the click of a button that is really just glass, or subtle cues during navigation and gaming.
Good haptics make touchscreens and controllers feel more responsive and can convey information without a sound or a glance, which also aids accessibility. The effect depends on quality hardware and thoughtful design, and overused buzzing simply annoys, so the best implementations are subtle, matching the feel to the action in a way people notice mostly when it is missing.