--- published: false --- # Glossary This page contains definitions for distribution related terms.

Blob: A blob is any kind of content that is stored by a Registry under a content-addressable identifier (a "digest").

Layers are a good example of "blobs".
Image: An image is a named set of immutable data from which a Docker container can be created.

An image is represented by a json file called a manifest, and is conceptually a set of layers. Image names indicate the location where they can be pulled from and pushed to, as they usually start with a registry domain name and port.
Layer: A layer is a tar archive bundling partial content from a filesystem.

Layers from an image are usually extracted in order on top of each other to make up a root filesystem from which containers run out.
Manifest: A manifest is the JSON representation of an image.
Namespace: A namespace is a collection of repositories with a common name prefix.

The namespace with an empty prefix is considered the Global Namespace.
Registry: A registry is a service that let you store and deliver images.
Repository: A repository is a set of data containing all versions of a given image.
Scope: A scope is the portion of a namespace onto which a given authorization token is granted.
Tag: A tag is conceptually a "version" of a named image.

Example: `docker pull myimage:latest` instructs docker to pull the image "myimage" in version "latest".