Images are blueprints for containers: layered filesystem snapshots plus metadata. Run docker run to start a container from an image; it starts instantly with everything pre-configured. Images are pulled from registries like Docker Hub and stored locally for reuse.
$ docker images # list local images $ docker pull <image> # pull an image from a registry $ docker rmi <image> # delete an image $ docker tag <image1> <image2> # retag an image $ docker search <image> # search Docker Hub
Each image has a name and tag (e.g., ubuntu:latest). The tag is usually a version or variant; latest is the default. Images are built in layers, where each layer adds or modifies files on top of the previous one. Layers are cached—rebuilding reuses unchanged layers, making builds fast.