The Unity Events Editor provides a way for programmers to expose C# events to the Unity Editor for use by designers. In addition to simply exposing and hooking into events via code like you normally would, designers may interact with these very same events through a simple visual editor.
You can define any number of "Event Responders" which become immediately available to the editor to be used with any applicable event.
This is a great way to quickly create tools that your designers can use to alter the behaviour of objects in your game instead of the constant back-and-forth that small changes can bring.