A card network token is a substitute card number, issued by a card network's token service, that is used in place of the real primary account number (PAN). Each token is limited to a particular merchant, device or channel and is sent with a one-time cryptogram. The token itself is the subject of this term; the process of issuing and using such tokens is network tokenization, which describes the roles, lifecycle and benefits in full.
Examples include tokens from the Visa Token Service and the Mastercard Digital Enablement Service, and the device tokens that sit behind phone wallets. The phrase "network token" is used to tell them apart from processor or gateway tokens, which are references inside a single company's vault and cannot be used with a different processor.
A card network token is one kind of payment token under the EMVCo framework. It has nothing to do with crypto tokens. Network tokens are widely used for card-on-file transactions because they update automatically when a card is reissued.