What is a blockchain?

A blockchain is a record structure that groups data into blocks and connects them using cryptographic hashes. Network participants validate new records under shared rules, maintaining a common transaction history.

Why are blocks linked together?

A block refers to the hash of its predecessor. Changing an earlier record affects that link, making accepted history much harder to alter than editing a single database entry. Security depends on the network’s validation rules and participants as well as its hash links. Describing the records as “impossible to change under any circumstances” hides those conditions.

For example, a Bitcoin transfer becomes part of the shared history when validated and included in a block. Later blocks build on that history. A user can read the record through a block explorer, but that interface is not the blockchain itself.

Is a blockchain the same as cryptocurrency?

No. Cryptocurrency refers to a digital asset; blockchain describes the record infrastructure. Not every blockchain has to be open to everyone like Bitcoin. Some networks restrict access to selected participants. Their design determines who can read and validate records.

Understanding the technology alone does not establish the value of an asset or the trustworthiness of a project using it.

Example

Imagine Alice’s payment recorded in block 100 and Sam’s later payment in block 101. In this simplified example, block 101 refers to the hash of block 100. Altering the earlier payment changes that hash, so the reference in the next block no longer matches. The network’s validation and consensus rules determine which history it accepts.