A token bridge is another name for a crypto bridge: a system that lets a user move tokens, or an equivalent claim on them, from one blockchain to another. The main entry explains bridge designs, security models and the major bridge hacks in detail.
The phrase "token bridge" stresses the asset being moved rather than general messaging between chains. In the common lock-and-mint design, the bridge holds the original tokens in a contract on the source chain and issues wrapped tokens on the destination chain; to return, the wrapped tokens are burned and the originals released. Other designs burn the token on one chain and mint it natively on the other, or use pools of liquidity on both sides. The resulting movement is described as a cross-chain transfer.
Some projects use "token bridge" as a product name for their own bridge, so the phrase can refer to a specific service. Whatever the label, the key risks are the same: the contracts holding locked funds are attractive targets for attackers, and the value of a wrapped token depends on the bridge staying solvent. The broader topic is covered under blockchain interoperability.