A blockchain transaction refers to the process of moving digital assets on a blockchain network. It involves creating a record of the transaction and adding it to a block in the blockchain, ensuring its immutability and transparency. Blockchain transactions are decentralized, meaning they do not rely on a central authority for verification and are secured by cryptographic algorithms.

So, a blockchain transaction happens when you send or receive digital assets over a network that isn't controlled by a single entity, which we call a decentralized network. This transaction triggers a piece of code in the network, leading to the execution of certain actions, like updating the balance in your digital wallet.