S3 provides a key-value store for objects; think of it as a really big HashMap in which you provide a key and store a blob of data as is. Data in S3 is managed through buckets which can contain an unlimited number of objects. Buckets are created with the regional scope and bucket names need to be unique because they are global and DNS compliant.

The naming rules for buckets which are as follows and can be found at https://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html.