Think of Bitcoin as a shared notebook that thousands of independent computers keep in sync. Transactions are gathered into blocks, and new blocks are added by miners who spend real electricity solving a computational puzzle, the mechanism known as <a href="/glossary/proof-of-work/">proof of work</a>. Once a block sits under enough later blocks, rewriting it becomes impractical, and that difficulty is what makes the ledger hard to tamper with.
The word does double duty. Capitalised, it usually means the network and the software; lower-case, it means the unit those rules govern. One coin divides into 100 million smaller units called <a href="/glossary/satoshi/">satoshis</a>, so nobody needs to buy a whole one. New coins enter circulation only as the reward paid to miners, and total issuance is capped at 21 million by the protocol itself.
Owning bitcoin really means holding the keys that authorise spending it. Coins left on an exchange are held by that exchange on your behalf, and moving them to a wallet you control transfers both the power and the responsibility to you. Our walkthrough on <a href="/toolkit/how-to-move-crypto-off-an-exchange/">moving crypto off an exchange</a> takes that step slowly, because it is the one where mistakes are permanent.
Be clear-eyed about the trade-offs. Transactions cannot be reversed: send to the wrong address and no support desk can retrieve the funds. Fees rise when the network is busy, confirmations are not instant, and the price moves sharply in both directions. None of that makes Bitcoin good or bad. It makes it a tool with sharp edges, worth understanding before any money is involved.
What Is Crypto and Blockchain? A Plain-English Start
Key takeaways
- Bitcoin's rules are enforced by software running on many independent machines, not by a company that can change them at will.
- You can own a fraction of a coin, since amounts are quoted in satoshis, so there is no minimum of one bitcoin.
- Whoever controls the keys controls the coins, which is why custody is the first thing to get right.
Bitcoin — frequently asked questions
Is Bitcoin the same thing as blockchain?
No. A blockchain is the general idea of a shared, append-only ledger maintained by many participants. Bitcoin was the first working example of one, but thousands of other networks now use the same basic pattern with different rules, different speeds and different trade-offs. Saying blockchain when you mean Bitcoin is a bit like saying engine when you mean one particular car.
Why is the supply capped at 21 million?
It is written into the protocol's issuance schedule. New coins are created only as a reward to miners, and that reward is cut in half at fixed intervals, so the total slowly approaches 21 million and then stops. The cap is a design choice about predictable scarcity rather than a guarantee about value, because a fixed supply says nothing about what demand will do.
New to crypto, or filling in the gaps? Work through the essentials in Learn, browse every term A–Z, or see live prices for the coins these concepts power.