A ZK Rollup (Zero-Knowledge Rollup) is a layer 2 scaling solution for blockchains, particularly for Ethereum. It allows for the processing of multiple transactions off-chain and then bundling them into a single transaction that is submitted to the main blockchain. This process is secured using zero-knowledge proofs, ensuring the validity and integrity of the transactions.

Key features of ZK Rollups include:

- Scalability: By processing transactions off-chain, ZK Rollups significantly increase the number of transactions per second (TPS) that can be handled, reducing congestion and improving performance.

- Security: ZK Rollups leverage the security of the main Ethereum chain. The zero-knowledge proofs ensure that the off-chain transactions are valid and have not been tampered with.

- Cost Efficiency: Because multiple transactions are bundled into one, the overall cost per transaction is reduced, making transactions cheaper for users.

- Data Availability: ZK Rollups ensure that transaction data remains available on-chain, which is essential for maintaining decentralization and enabling users to verify the state independently.

- Interoperability: ZK Rollups maintain compatibility with Ethereum, allowing existing smart contracts and applications to function without modifications.

In summary, ZK Rollups aim to improve the scalability and efficiency of blockchain networks like Ethereum while maintaining high levels of security and decentralization.