Cascade is a waterfall white-noise player. It runs on several platforms. The public product is the player, not the architecture that makes those platforms possible.
Cascade: A waterfall white-noise player for focus, prayer, and sleep. Avoid: pitching Cascade as an architecture kata in user-facing copy
Core: The headless Rust state machine that owns Cascade's behaviour. It has no audio, filesystem, or clock. Avoid: backend, engine (when meaning this)
Shell: A native client around the core. Each shell owns side effects — audio, OS integration, and UI. Avoid: using "platform" for the client; using "shell" in user-facing copy
App: The user-facing Cascade product on a device — what someone opens, downloads, or installs. The word a visitor sees. Avoid: using "app" for the core
Platform: The operating system or device family a shell targets: web, Android, macOS, Windows, iOS, watchOS. Avoid: using "platform" for the shell itself
Watch app: The Apple Watch client. It is not independently installed; it comes with the iPhone app.