What is the Lightning network?
The Lightning network is a Layer 2 scaling solution for Bitcoin and the blockchain. It is designed to enable fast, cost-effective off-chain bitcoin transactions while scaling very well, unlike the blockchain. The Lightning network is not a separate and standalone project, but builds as an extension directly on the Bitcoin / Blockchain infrastructure. The Lightning network is thus part of Bitcoin.
The Lightning network is still an experiment, but many Bitcoin experts are counting on the potential. The following links should help to better understand Lightning and to estimate the potential of the concept itself.
Basics
Lightning Network Whitepaper - https://lightning.network/lightning-network-paper.pdf
Lightning Network Website - https://lightning.network/
Presentation:
Technical Presentation:
https://upload.wikimedia.org/wikipedia/commons/6/67/Technisch_korrekte_aber_stark_vereinfachte_Erkl%C3%A4rung_des_Lightning_Netzwerkes.pdf
Helpful videos
Lightning-Network on the 1th of May, 2018.