Fundamentally, Stellar is a system for tracking ownership. It uses an accounting ledger, shared across a network of independent computers, to store two important things for every account holder: what they own (their account balances) and what they want to do with what they own (operations on those balances, like buy or sell offers). The computers that run Stellar and publish the ledger are called nodes. They systematically validate the ledger’s contents so it’s always consistent across the network. For example, when you send someone a dollar on a Stellar-built app, the nodes check that the correct balances were debited and credited, and each node makes sure every other node sees and agrees to the transaction.