Account Model
In the account model (used by Ethereum), each address has a running balance that transactions increase or decrease.
In depth
It works like a bank account: send 2 ETH and your balance simply drops by 2 (plus fees). This is simpler for smart contracts, which need to track state, but requires a nonce to prevent the same transaction from being replayed. Most smart-contract platforms use this model.
Why it matters
Knowing which model a chain uses helps you read explorers and understand fee behaviour.