Bitcoin’s blockchain is *append-only*, meaning that once a block is embedded in the chain, it is practically infeasible to remove or alter it. This makes Bitcoin’s history immutable.

Initial Block Download or IBD is the process of building the full Bitcoin blockchain from scratch. When a new node is set up and joins the network, it connects to other nodes and asks them for blocks.

A Lightning invoice serves as a request for payment and includes the amount to be paid and the destination of the payment.