Lightning is a decentralized network using smart contract functionality in the blockchain to enable instant payments across a network of participants.
Problem
Bitcoin transaction is slow and will be more slow in future because its popularity and many transactions
Bitcoin transaction fee is expensive and will be more expensive
Lightning Network can help
Instant Payments. Lightning-fast blockchain payments without worrying about block confirmation times. Security is enforced by blockchain smart-contracts without creating a on-blockchain transaction for individual payments. Payment speed measured in milliseconds to seconds.
Low Cost. By transacting and settling off-blockchain, the Lightning Network allows for exceptionally low fees, which allows for emerging use cases such as instant micropayments.