Lightning network: The Lightning Network extends Bitcoin with payment channels to increase transaction speed and lower costs. It is becoming widely adopted and accepted as the preferred way to scale Bitcoin.
Payment: A payment is a transaction that occurs over the Lightning network. Payments are routed through Lightning payment channels and are not recorded in the Bitcoin blockchain.
Transaction: A transaction is a transfer of value over the Bitcoin network. While transactions can be complicated, one of the simplest forms of a transaction would be sending bitcoin from one address to another. A transaction is not considered final until it has been included in a valid block by a miner.