A card token is a general term for a value that stands in for a real card number, and its most important form, issued by the card schemes, is described under card network token. Tokens let merchants, wallets and processors handle payments without storing or transmitting the actual primary account number.
There are two broad kinds. Network tokens are created by the card network's token service at the request of a token requestor, such as a mobile wallet or merchant. They are format-preserving numbers that can be used for authorisation, are limited to a device, merchant or channel, and come with dynamic cryptograms. Mobile wallets store them in place of the card number, and card-on-file merchants use them so that payments keep working when a card is reissued. Gateway or processor tokens, by contrast, are references created by a payment provider for its own vault; they can only be used with that provider and are mainly a security and PCI scope tool.
When people say "card token" they may mean either kind, so the context matters. Both fall under the wider practice of payment tokenization, and network tokens are managed through token lifecycle management.