Physical unclonable function

A physical unclonable function, or PUF, is a physical object whose operation cannot be reproduced ("cloned") in physical way (by making another system using the same technology), that for a given input and conditions (challenge), provides a physically defined "digital fingerprint" output (response) that serves as a unique identifier, most often for a semiconductor device such as a microprocessor or a material producing an optical signal. PUFs are often based on unique physical variations occurring naturally during semiconductor manufacturing.

Source: Wikipedia — Physical unclonable function (CC BY-SA 4.0)