A Docker image is a read-only template containing application code, runtime, libraries, and dependencies. A Docker container is a running instance of an image.
Key differences:

• Images are immutable blueprints; containers are mutable runtime environments
• Images are stored; containers are executed
• Multiple containers can be created from a single image
• Changes to containers don't affect the original image
  Example:

# Image exists as a template
docker images
# Container is created and runs from image
docker run nginx