Atomicity, Consistency, Isolation, Durability - properties that guarantee database transactions are processed reliably. Like having strict rules that ensure bank transfers either complete fully or not at all.
When you transfer money between accounts, ACID properties ensure the money is either transferred completely or the transaction fails entirely.
ACID is a set of transaction guarantees (Atomicity, Consistency, Isolation, Durability), not a cloud service. Many managed relational databases and some distributed databases across AWS, Azure, GCP, and OCI provide ACID transactions, but the exact guarantees and scope (single row, single database, cross-shard, cross-region) vary by product and configuration.