A transaction is a digital exchange of value between two parties, also known as peer-to-peer (P2P). It uses a distributed ledger, known as a blockchain, to track and verify transactions. This ledger is decentralized and publicly available, meaning that anyone can view it, but only the participants involved in the transaction have access to the private keys necessary to authorize and complete it.
A blockchain transaction typically involves the transfer of cryptocurrency, such as bitcoin or ether, from one user to another. The transaction is broadcast to a network of computers, known as nodes, and each node validates the transaction using its individual copy of the blockchain ledger.
Once the transaction is verified, it gets added to the ledger and is then considered confirmed and immutable. Since all nodes on the network have access to the same shared ledger, a malicious actor would need to control more than half of the total computing power on the network in order to alter the blockchain.
This is known as the 51% attack, and is virtually impossible to achieve without significant resources. As such, blockchain transactions are considered secure and reliable, making them ideal for many types of digital financial activities.