Amazon Simple Storage Service is AWS's object storage service, launched in 2006 as one of the first AWS products. S3 stores arbitrary binary blobs organized into buckets and retrieved by key, with per-object durability of eleven nines (99.999999999 percent) and effectively unlimited capacity.
S3's interface has become a de facto industry standard. Google Cloud Storage, Azure Blob Storage, MinIO, and dozens of smaller providers all expose S3-compatible APIs. The "S3-compatible" moniker has become shorthand for any object storage service that a standard S3 client can talk to without modification.
For AI workloads, S3 (and its equivalents) is the standard storage layer for training data, model checkpoints, and inference outputs. The combination of near-infinite capacity, predictable cost, and broad tool support makes it the default destination for any data large enough to exceed database-friendly scale.