Lightning Network is a second-layer protocol on top of a blockchain that uses off-chain payment channels, cryptographic scripts, and on-chain enforceability to provide near-instant, scalable transactions without relying on custodians

Quotes that support claims

The Lightning Network is dependent upon the underlying technology of the blockchain. By using real Bitcoin/blockchain transactions and using its native smart-contract scripting language, it is possible to create a secure network of participants which are able to transact at high volume and high speed.

Lightning is a decentralized network using smart contract functionality in the blockchain to enable instant payments across a network of participants.