What is a Bitcoin transaction?
A signed instruction that moves bitcoin: it spends some earlier outputs and creates new ones, each with an amount and an owner.
A transaction is the only way bitcoin moves. It names the pieces being spent (its inputs), proves with signatures that the sender may spend them, and creates the new pieces (its outputs), usually a recipient and change back to the sender.
Once broadcast, a transaction waits in the mempoolMempoolThe waiting room for Bitcoin transactions that have been sent but aren't in a block yet. until a miner includes it in a block. It gets a transaction ID when it's made, so you can follow it from sending to confirmation.