The Lightning Network is a micropayment protocol for sending small amounts of Bitcoin instantaneously and with almost no fees.
It is a “Layer 2” protocol that operates on top of the Bitcoin network and uses its security. It allows the Bitcoin network a way to scale to thousands of transactions per second.
The Lightning Network uses payment channels to send money from user to user. When you want to send money to another person, they send you an invoice for the exact amount, similar to shopping online. You then process the invoice and funds are sent from your wallet to theirs.