ACID-rules

Atomic (Atomic): The degree to which the DBMS guarantees that a transaction is either fully executed or completely null and void.
Consistent: A transaction either creates a new valid state or restores the state that was there (in case of an error or problem). This implies that after the transaction all integrity rules of the database must apply. [1]
Isolated: transactions are executed in isolation from each other, that is, transactions that are executed simultaneously have no insight into each other's intermediate results.
Durable: a completed transaction cannot be invalidated later.