What is the difference between Aura Custom Events and Lightning Message Service?

Aura Custom Events: Component events (bubble up the component tree) and Application events (broadcast to all registered listeners in the page). Application events in Aura are global broadcasts — any component on the page listening for that event receives it, regardless of hierarchy. This creates tight coupling and potential performance issues. Lightning Message Service (LMS): The modern standard for cross-component communication in both LWC and Aura. Uses a declarative Message Channel definition. Components subscribe to specific channels, reducing global pollution. LMS works across all UI frameworks (LWC, Aura, Visualforce in Lightning). Preferred over Aura Application Events for new development. LMS supports scoping (active tab only) and is more performant. Migrate Aura Application Event-based communication to LMS.