21 million
The hard cap on how many bitcoin will ever exist. No one can raise it, which is the whole point.
Go deeper →Bitcoin words, translated.
Every technical word on this site, explained in one plain sentence. Wherever you spot a dotted underline, tap it for the same answer without leaving the page.
2
A
Address
The code you share so someone can send you bitcoin, like an account number, safe to give out.
Go deeper →Altcoin
Any cryptocurrency that is not Bitcoin. Thousands have been launched, and most of them are already gone.
Go deeper →B
Bitcoin
Digital money that works without banks: it runs on a public network no company controls, 24/7, worldwide.
Go deeper →Bitcoin ETF
A stock-market product that tracks Bitcoin’s price. You own a share of a fund, not bitcoin, and you hold no keys.
Go deeper →Block
A batch of transactions added to the ledger together, roughly every ten minutes. Chain the blocks and you have the blockchain.
Go deeper →Block reward
The new bitcoin paid to whoever mines a block. It halves every four years and is how all bitcoin enters circulation.
Go deeper →Blockchain
The public ledger every Bitcoin transaction is recorded on. Thousands of computers keep identical copies, which is why nobody can cheat it.
Go deeper →C
Change address
When you spend a piece of bitcoin larger than you need, your wallet sends the remainder back to an address it owns. Nothing is lost.
Go deeper →Confirmation
Each new block built on top of yours makes your payment harder to undo. One confirmation is usually fine for small amounts.
Go deeper →Custodial
A service that holds your bitcoin and its keys for you. Convenient, but you have to trust them and ask permission to use your own money.
Go deeper →D
Decoy wallet
A second wallet with a small balance you can show under pressure, keeping your real savings hidden.
Go deeper →Dollar-cost averaging
Buying a fixed amount on a regular schedule instead of all at once, so the price you pay averages out over time.
Go deeper →Dust
An amount of bitcoin so small that spending it would cost more in fees than it is worth.
Go deeper →E
Entropy
The randomness a wallet draws on to create your seed phrase: with enough of it, nobody can ever guess your words.
Go deeper →Exchange
A business where you swap regular money for bitcoin. Most hold your coins for you until you withdraw them to your own wallet.
Go deeper →Extended public key
A key that can generate all your receiving addresses without being able to spend anything. It is how watch-only wallets work.
Go deeper →F
Fiat
Ordinary government money: dollars, euros, pounds. Called fiat because its value comes from decree rather than scarcity.
Go deeper →H
Halving
Roughly every four years the reward for mining is cut in half, so new bitcoin arrives more slowly until the last one is mined.
Go deeper →Hardware wallet
A small offline device that keeps your keys away from the internet: the safest home for savings you don’t touch often.
Go deeper →Hot wallet
A wallet on a device that’s connected to the internet, like your phone. Convenient for everyday amounts.
Go deeper →K
Keys (private key)
The secret that proves your bitcoin is yours and lets you spend it: whoever holds the keys controls the money.
Go deeper →KYC
“Know Your Customer”: the identity paperwork (ID, selfie, proof of address) most exchanges require before letting you buy.
Go deeper →L
Lightning Network
A faster layer built on top of Bitcoin for small, instant, nearly-free payments.
Go deeper →M
Mempool
The waiting room where transactions sit before they make it into a block. When it is crowded, fees go up.
Go deeper →Mining
The worldwide competition to add the next page to Bitcoin’s ledger. The winner earns new bitcoin, which is how coins are created.
Go deeper →Multisig
A wallet that needs several keys to approve a payment, so losing or leaking any one key is not a disaster.
Go deeper →N
Network fee
A small amount paid to the Bitcoin network (not to us) to process your transaction. It varies with how busy the network is.
Go deeper →Node
A computer running Bitcoin’s rules and keeping its own copy of the ledger. Thousands of them, run by ordinary people, are what make the network hard to push around.
Go deeper →O
Open source
Software whose full code is published for anyone to read, check, and copy. No blind trust required.
P
Passphrase
An extra word of your own added to a seed phrase, opening a separate hidden wallet. Powerful, and unrecoverable if you forget it.
Go deeper →Proof of work
The costly computing race that secures Bitcoin: rewriting history would mean redoing all that work, which nobody can afford.
Go deeper →Public key
The shareable half of a key pair. Your addresses come from it, and it can never be used to spend your bitcoin.
Go deeper →R
Replace-by-fee
A way to un-stick a slow transaction by re-sending it with a higher fee. Same payment, better place in the queue.
Go deeper →S
Satoshi Nakamoto
The pseudonym of whoever published Bitcoin in 2008 and then disappeared. Nobody knows who they were, and the network runs fine without them.
Go deeper →Sats (satoshis)
The smallest unit of bitcoin: 100 million sats make one bitcoin, so you can start with a tiny amount.
Go deeper →Seed phrase
The 12-24 words that back up your wallet: anyone who has them controls your bitcoin, so you never share them.
Go deeper →Self-custody
Holding your bitcoin with your own keys instead of trusting a company to hold it for you: cash in your pocket, not money in someone else’s vault.
Go deeper →U
UTXO
An unspent piece of bitcoin sitting in your wallet, a bit like a banknote of an odd amount that you can only spend whole.
Go deeper →V
Volatility
How sharply a price swings. Bitcoin’s is high, which is why it is a poor place for money you need next month.
Go deeper →W
Wallet
An app or device that holds the keys to your bitcoin and lets you send and receive it. The bitcoin itself lives on the network.
Go deeper →Watch-only
A wallet you can look at but not spend from: it knows your addresses, while the keys stay somewhere safer.
Go deeper →