Cancelled state - by: antonio.grr

Hi.
Could you please explain me the exact meaning of cancelled status ?
I assumed to use it when an item is no more used but I don't want delete it from db to keep trace of it. But it sound strange to me when, selecting cancel fro an item ( say a Ticket), I'm requested to complete the item. What happens where I cancel a ticket having real work on it ?
Thank you for your attention.