If you’ve heard different key terms for Docker’s building blocks but don’t fully grasp what they mean, we’ve prepared this list to help act as a reference and keep a mental image of what’s going on.

To start, Docker borrows concepts from the shipping container industry, and knowing this helps to remember how the components fit together.


Docker images are the basis of containers. An Image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime. An image typically contains a union of layered filesystems stacked on top of each other. An image does not have state and it never changes.

Shipping Container Analogy:

Think of an image as a blueprint, or a manifest which might list what goes in to a container, and how it’s contents are organized.


A container is a runtime instance of a docker image.

A Docker container consists of:

  • A Docker image
  • An execution environment
  • A standard set of instructions

Shipping Container Analogy:

The concept is borrowed from Shipping Containers, which define a standard to ship goods globally. Docker defines a standard to ship software.

There are many docker terms and concepts and we might expand this list as we go.

For an exhaustive list of definitions, see Docker’s full glossary: