Bitcoin's ordered, proof-of-work-protected record of blocks.
Block chain meaning
The block chain is the history independently accepted by a node after it validates every relevant rule. Each block header refers to the one before it, creating a chronological chain. The term is often written as one word in general use, but Bitcoin's developer documentation also uses two.
How it works in Bitcoin
Nodes compare valid competing histories by accumulated proof of work, not by counting votes or trusting the first server they contact. A node stores the history it has verified and updates its best chain as new valid work arrives.
A simple example
Two miners can occasionally publish blocks at nearly the same time. The network may briefly have two tips. When more valid work extends one branch, nodes converge on that branch and the other block becomes stale.
Why Block chain matters
Network terms explain how independently operated software shares, validates and orders information. They help separate a convenient data viewer from the rules a node actually enforces.
What people often get wrong
A block explorer is a convenient view into chain data, not the blockchain itself and not an authority that decides whether a transaction is valid.
Quick checks before using the term
- Which actor performs this job?
- Is the behavior a consensus rule or an implementation choice?
- What evidence can a node verify independently?
Apply these questions to the concrete example above. A precise answer is more useful than repeating the definition without naming the actor, rule or failure path.
Check the primary reference
This entry is written in plain English, but the technical source is available when you need exact protocol detail.
Bitcoin Developer Guide: Block Chain ↗