--- draft: true --- # 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 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 and other content.

#### 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".