A blockchain is a digital ledger system used to securely record transactions across multiple computers. You can think of it like a public notebook where everyone can see the information, but no one can modify it without the consensus of others.

Each transaction is stored in a "block," and these blocks are connected to form a "chain." This structure makes it nearly impossible to alter or delete any information once it’s recorded, which ensures the system is secure and trustworthy.

Because of this, blockchains are used in many applications where security and transparency are important. Some well-known blockchains include Bitcoin, Ethereum, Solana, and TRON.