The process of identifying the same user across different devices via a unique and persistent identifier, such as an email address.
Thanks to deterministic matching, advertisers, AdTech platforms and Publishers are able to identify users across different devices, browsers, and channels, allowing them to improve Ad targeting, analytics and Attribution.
Applications like Facebook, Google Apps and Twitter can deterministically match users on different devices (smartphones, laptops, tablets, etc.) as they require them to sign in with an email address to access their services across different devices.
Also see Probabilistic matching.