A Lightning Network invoice is a payment request that utilizes the Lightning Network, a layer-2 protocol  built on top of the Bitcoin blockchain. Unlike Layer 1 Bitcoin blockchain transactions, Lightning Network transactions occur off-chain, allowing for faster and cheaper transactions. 

When someone requests a payment over the Lightning network, they send an “invoice.” Lightning Network invoices include a payment amount, a payment request code, and an expiration time.  It also contains information about the destination of the payment, a memo field, and other metadata. Invoices are created by the payment recipient and can be sent to the payer through various means, such as email, messaging apps, or QR codes.

To make a payment using a Lightning Network invoice, a payer with a Lightning Network-enabled wallet scans the invoice or otherwise inputs it (e.g., by copy and paste) it into their wallet to initiate the payment. The payment is then routed on the Lightning Networks until it reaches the recipient's wallet.

The Lightning Network offers several advantages over layer-1 Bitcoin  blockchain transactions.

First, Lightning Network transactions occur off-chain, meaning they do not have to be recorded on the blockchain. This allows for faster transactions and lower fees, making it possible to facilitate small transactions that would otherwise be impractical on the blockchain.

Second, the Lightning Network offers improved scalability for blockchain networks. By reducing the number of transactions that need to be recorded on the blockchain, the Lightning Network can alleviate congestion and reduce network fees. This makes it easier for the Bitcoin blockchain to handle increased transaction volume, enabling them to support more users and applications.

Finally, the Lightning Network offers greater privacy  to its users. Lightning Network transactions occur directly between users and are not publicly broadcasted on the blockchain. This helps to protect user privacy by reducing the amount of transaction information that is publicly available.

In summary, a Lightning Network invoice is a payment request used in the Lightning Network to facilitate faster, cheaper, and more scalable transactions on top of the Bitcoin blockchain.

What Is The Lightning Network, And Why Is It Important?
The Lightning Network is a network of computers that lets people transfer their bitcoin more quickly, and with much lower fees.
How Is the Lightning Network Transforming How People Use Bitcoin?
The Lightning Network solves the problem of limited bitcoin throughput on the blockchain and drastically reduces transaction fees for small payments.
What Is A Lightning Network Channel?
A Lightning Network channel is a two-way connection between two parties that enables them to exchange funds.