What Is a Blockchain?

Imagine a ledger where, instead of one office keeping the master copy, thousands of strangers around the world each keep an identical copy and constantly compare notes to make sure none of them has quietly changed a page. That's the basic idea behind a blockchain: a record of transactions maintained collectively rather than by a single authority.

What makes it different from a normal database

A typical database — the one behind a bank account or an online store — lives on servers one organization controls. That organization can edit records, restrict access, or go offline, and users have no independent way to check whether the data was changed. A blockchain instead organizes transactions into blocks that link to the one before them, and distributes identical copies of that chain across many independent computers, called nodes. Adding a new block requires those nodes to independently verify and agree on it, and altering a past block would require redoing that agreement across enough of the network to be practically impossible.

Why the distribution is the whole point for self-custody

Because no single company keeps the authoritative version of a blockchain, no single company decides who's allowed to hold or move an asset on it — that authority comes down to whoever holds the private key tied to an address. It also means the record doesn't depend on any one computer staying online: as long as enough independent copies exist, the ledger keeps functioning even if individual nodes shut down. That distributed structure is what makes self-custody possible in the first place, since there's no institution in the loop to grant or revoke access.

For the credential that actually authorizes moving an asset on this kind of network, see What Is a Private Key?, and for how individual confirmations get added to the chain, see What Is a Block?