AWS's object storage service. It stores objects in buckets with 99.999999999% durability (11 nines). It supports multiple storage classes based on access frequency: Standard, Intelligent-Tiering, Glacier.
On CLF-C02 this is the object storage example. SAA-C03 covers lifecycle policies, versioning, replication, and storage classes. Question: which class for files accessed rarely but needing immediate access? S3 Standard-IA.
S3 (Simple Storage Service) is a concept that can show up on the exam. Check the full guide to see it in context.