Transaction guarantees: atomicity (all or nothing), consistency (data moves from one valid state to another), isolation (concurrent transactions don't interfere), and durability (committed changes aren't lost even if the system fails).
In DP-900 you are asked which property applies in a scenario: a transfer that is fully undone if the credit fails is atomicity; an order that remains saved after a power outage is durability.
ACID properties is a concept that can show up on the exam. Check the full guide to see it in context.