A — Atomicity Definition: A transaction is all-or-nothing. It either completes fully or doesn't happen at all. Example: In a banking app, transferring ₹500 from Account A to B involves debiting A and crediting B. If one step fails, neither change is saved. C — Consistency Definition: A transaction brings the database from one valid state to another valid state, preserving data integrity. Example: If a rule says an account cannot be negative, the system will ensure that no transaction results in a negative balance. I — Isolation Definition: Transactions are independent of each other. Concurrent transactions do not interfere with one another. Example: If two users book movie tickets at the same time, each transaction should happen as if it's the only one in the system. D — Durability Definition: Once a transaction is committed, the changes are permanent, even if the system crashes. Example: After a successful order is placed in an online store, it remains recorded even after a sudden power outage.