What is a Docker Image and why is it used in containerization?

A Docker Image is a template or snapshot of a filesystem and settings that contains everything needed to run an application: code, libraries, dependencies, and system tools. It is used in containerization to create isolated, reproducible, and portable containers.

When a container is launched, Docker uses the image as a base, creating an instance with its own state. This ensures that the application will run the same way in any environment — on a local machine, a server, or in the cloud.

Example: an image can contain a web server with an application and all dependencies, which can be quickly deployed on any server without additional configuration.