ACID stands for: Atomicity: Ensures that all operations within a transaction are completed; if not, the transaction is aborted. Consistency: Ensures that the database remains in a consistent state before and after the transaction. Isolation: Ensures that transactions are isolated from each other until they are completed. Durability: Ensures that once a transaction is committed, it remains committed, even in the event of a system failure. Why Some Databases Need ACID: Databases that require strong data integrity and reliability, such as financial systems, need ACID properties to ensure data consistency and reliability. Why Some Databases Don't Need ACID: Some databases, especially in NoSQL systems, prioritize availability and scalability over strict consistency. These databases might use eventual consistency models instead of enforcing ACID properties.