They are called flight time cameras. In English, the acronym TOF, which is likely to be more successful, from the point of view of marketing.
And it refers to an infrared camera that emits a light pulse and then measures the time that elapses between leaving the camera until it reflects back on an object and returns to the sensor.
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As a radar of infrared light (that is invisible to the human eye); or as a Lidar, which does something similar with a laser, widely used in autonomous cars.
The TOF camera is not a very new technology, but it is new that in recent months several mobile phone companies have included this technology in their equipment.
The version that the iPhone X uses is called TrueDepth:
An infrared light illuminates the user's face by 30,000 points and an infrared camera photographs the face, determines the position of those points and compares it with a previous record to confirm that it is the right person.