A browser-based command line terminal that comes pre-loaded with cloud management tools, letting you manage cloud resources directly from your web browser without installing anything on your computer. Like having a fully-equipped workshop that appears anywhere you open your laptop.
A DevOps engineer uses Google Cloud Shell to quickly debug a production issue from their phone during vacation — they open a browser, get instant terminal access with gcloud, kubectl, and terraform pre-installed, fix the Kubernetes deployment, and close the tab.
All four are browser-based terminals authenticated to your cloud account and preloaded with common CLIs/SDKs so you can manage resources without installing tools locally. Differences are mainly in default tooling, storage persistence, and session limits.