iFixit:

Put simply, haptic feedback recreates the sense of touch or movement in an otherwise immovable or shallow-clicking object, like a button or trackpad. This is accomplished with a vibration motor, emitting controlled bursts of bzzzt as you tap and press. Apple has branded its own vibration motor the Taptic Engine.

And:

What makes Apple’s Taptic Engine different from other haptic applications we’ve seen over the years is the precise engineering Apple has put into it, and the precious space they devote to it inside their increasingly tight devices. Given this effort, Apple has come closer than any firm at actually replacing the tactile mechanical buttons some of us might miss.

And:

When the weighted mass inside a vibration motor moves back and forth at just the right speed, the vibration effect produced by the motor is amplified across the whole phone.

And:

Apple tunes their Taptic Engines to resonant frequencies optimized for quick, precise taps; and since they are designed in-house, they can pick specific sizes, shapes, and resonant frequencies for each product. In contrast, other smartphone manufacturers are at the mercy of whichever vibration motor manufacturer they happen to be purchasing from.

It’s those tiny details. No one is better than Apple at identifying and implementing those details in fit and finish. And I hear some of you in the back shouting “Butterfly keyboard”. Yes, but the keyboard issues are most notable because they are glaring exceptions to what we’ve come to expect from Apple.

Fascinating read.