TOPIC: Creating a hidding text area field for an event

Is there a way to create a hidden text area field for an event? I can do it for an individual user registered for the program, but looking for something more global.

Basically, I want to create a field where the person running an event can go in and leave a note about that event, at any point after the event has been created. That way, when we export the records for the event the note is associated with it.