What's the difference between websites, stores, and store views in Magento?

Magento has three scopes:

• Website — isolation boundary for customers, carts, orders and (by default) prices. Use one website per legal entity / region with separate carts.
• Store — root-category boundary. Use multiple stores per website when you need different catalog trees (e.g. brand A vs brand B sharing a checkout).
• Store view — locale boundary. Use one per language inside the same store (e.g. EN, FR, DE views of the EU store).

Wrong-scope configuration is the #1 source of multi-store pain. We map the hierarchy in the audit before any code is written.