What is ACID Transactions?
ACID is a set of four guarantees, atomicity, consistency, isolation and durability, that make database transactions reliable.
ACID Transactions explained
Atomicity means a transaction happens completely or not at all. Consistency means it moves the database between valid states. Isolation means simultaneous transactions do not interfere. Durability means once committed, the result survives a crash.
These guarantees are why a transfer between two accounts cannot leave money deducted from one and never added to the other.
Example
Recording an order, reducing stock and creating an invoice inside one transaction means a failure halfway rolls all three back.