Bucket
A bucket is a top-level container that holds objects in cloud storage, identified by a globally unique name. It's an Amazon S3 term — since adopted by many S3-compatible services — that sets a namespace and boundary for permissions, region, and configuration. Every stored object belongs to exactly one bucket.
In S3 and S3-compatible systems, you can't store an object without first creating a bucket to put it in. The bucket name lives in a global namespace (no two accounts can share one), and it anchors a lot of configuration: which region the data lives in, who can access it, lifecycle and versioning rules, and public-vs-private defaults.
Because so much policy attaches at the bucket level, bucket sprawl and misconfiguration are a classic source of cloud incidents — a single 'public' toggle on the wrong bucket has caused many well-known data leaks. Designing your bucket layout and access policy is real architectural work.
The term is specific to the object-storage world. A traditional file system has directories, not buckets; the bucket abstraction exists to give a flat object store a top-level ownership and configuration boundary.