The ACID model defines core properties for database transactions: Atomicity, Consistency, Isolation, and Durability. These principles ensure data reliability in systems handling money, inventory, or critical records. A transaction acts as a single logical unit, preventing partial updates that could corrupt state.

Atomicity guarantees an all-or-nothing outcome, using rollbacks if any operation fails. Consistency enforces business rules and constraints, rejecting invalid states. Isolation shields concurrent transactions from interference, preventing dirty reads and phantom data. Durability commits changes permanently, surviving crashes via logs and replication.

For financial and e-commerce platforms, ACID compliance is non-negotiable. While modern distributed systems sometimes trade ACID for performance, understanding these trade-offs is essential. Choosing the right isolation level balances safety against cost. Developers must weigh these fundamentals when designing reliable data layers.