Lighting Network is a Layer 2 scaling solution for blockchain-based platforms. Designed to allow for the creation of off-chain payment channels by leveraging HTLC (Hash-Timelocked-Transaction) smart contracts, the Lightning Network is able to offer micro-transactional capabilities and a fees structure that is orders of magnitude cheaper.
Initially, the Lighting Network was intended to service the Bitcoin blockchain, it has since expanded and become blockchain agnostic meaning that is can be implemented as a solution on top of any blockchain.
What is exciting in the approach of the Lighting Network in solving the scaling problem is the verifiable guarantee that in the event of any security breach or other malicious network failure, funds will fall back onto the first layer safely.