One or more atoms with the same number of protons (atomic number) but a different number of neutrons. 

ISO 22381:2018

An ISO guidance standard for establishing interoperability among object identification systems to deter counterfeiting and illicit trade.

ISO 22382:2018

An ISO guidance standard for the content, security, issuance and examination of excise tax stamps.

ISO 22383:2020

An ISO guidance standard for the selection and performance evaluation of authentication solutions for material goods”

Interference (light)

The result of the interaction of two intercepting light waves. Interference pigment flakes are used in colour-shifting inks and interference foils with colour-shifting properties also exist.