The name of an S3 bucket must be unique _________.

The name of an S3 bucket must be unique worldwide across all AWS accounts. This means that no two S3 buckets can have the same name, regardless of the account in which they are created or the region they reside in. This global uniqueness requirement is crucial because S3 is a highly available and scalable object storage service, and it allows AWS to ensure that requests to a bucket are directed to the correct resource.

For instance, if one user creates a bucket called "my-unique-bucket," no other user, in any AWS account, can create a bucket with that same name. This standard helps avoid conflicts and confusion in naming and accessing S3 buckets across the entire AWS ecosystem.

The other options suggest limitations in uniqueness, such as being confined to a specific region or AWS account. However, these do not meet the requirement, as the intended design of S3 necessitates having a globally unique naming system to prevent potential conflicts and support the global nature of the service.