While the advent of Bitcoin (BTC) has been revolutionary in terms of it being decentralized, immutable and permissionless there are a couple of drawbacks. The first is that it takes time to process the transactions and the second is that it is not economically viable for micro payments (a few cents).
The Lightning Network was developed to solve these problems so that Bitcoin (currently Lightning is Bitcoin only) can be used effectively at Point of Sale (POS) terminals in cheap, fast and private transactions. Lightning is what is called a Layer 2 protocol meaning that it rides on top of the Bitcoin Blockchain.
The Lightning Network site is linked here: https://lightning.network/#intro
The rapid adoption of the Lightning network is evidenced by Square/Cash App and Strike announcing their integration with the Lightning network.
A good, updated article on adoption of Lightning is here: https://bitcoinmagazine.com/business/the-state-of-lightning-network-adoption.
Please let us know if you have any questions on Lightning in particular or Blockchain and crypto, in general.
All the best…Chris