In case of high interest and large trading volume, it can take a very long time to get a Bitcoin transferred from one wallet to another, due to low block size of the Bitcoin blockchain. So in order to make transactions on the Bitcoin blockchain faster, the Lightning Network has been developed.
Lightning network works as a second layer, on top of the blockchain and it can handle transactions without the need to make them all public in the blockchain, thus saving a lot of resources. This is extremely handy especially in case of micro/small transactions, where the cost of the transaction could exceed the value transferred. Such transactions are still secure, thanks to the utilization of smart contracts.
For more information, visit the official Lightning Network site : https://lightning.network/