Block

A block is a batch of confirmed bitcoin transactions bundled together with a header and appended to the blockchain. New blocks are produced by miners roughly every 10 minutes, can hold up to 4 million weight units of transaction data, and each one references the block before it, forming an unbroken chain back to the genesis block of January 2009.

Why it matters

Blocks are the unit of settlement in Bitcoin. A transaction sitting in the mempool is only a proposal; once it is included in a block it is confirmed, and each additional block built on top makes reversing it exponentially more expensive, since an attacker would need to redo the accumulated proof of work. Six confirmations, about an hour, is the traditional standard for treating large payments as final. Blocks are also the unit of monetary issuance: each new block currently creates 3.125 new bitcoin as the block subsidy, the only way new coins enter circulation.

In the gold vs bitcoin debate

Settlement speed separates the two assets sharply. Physically settling a gold trade means moving and re-assaying metal, which is why most gold trading settles as paper claims inside systems like the London bullion market. Bitcoin achieves final settlement of any amount, across any distance, in about an hour of block confirmations, without a vault, courier, or clearinghouse. Gold advocates respond that gold's settlement has worked for millennia and requires no electricity or network to remain valid.