ZK-Rollups is a layer-2 scaling solution for Ethereum, and it helps in scaling the Ethereum network by reducing the amount of computation and data that needs to be stored on-chain.

ZK stands for "Zero Knowledge" which refers to the ability to prove that certain information is true without revealing that information. In the context of ZK-Rollups, zero-knowledge proofs are used to validate a large number of transactions off-chain and then submit a single "proof" to the main Ethereum chain. This proof is called a "rollup".

A ZK-Rollup takes multiple operations, such as transfers or smart contract calls, rolls them up into a single transaction, and then generates a cryptographic proof, known as a SNARK (Succinct Non-Interactive Argument of Knowledge). This proof is submitted to the blockchain, and it is then able to validate all of the operations within it without having to individually execute them. This reduces the computation required by the Ethereum network, leading to a decrease in transaction costs and an increase in throughput.

The big advantage of ZK-Rollups is that they don't compromise on security. The rollup's data is stored on-chain, making it as secure as the Ethereum mainnet itself. And because the proofs are verified by the network, even if the entity performing the rollup tries to cheat or goes offline, the funds and data inside the rollup are safe.

As of my knowledge cutoff in September 2021, Ethereum is developing and integrating various layer-2 solutions, including ZK-Rollups, to deal with the scalability issue. However, the specific progress or any new development after that period is something I won't be able to provide.