As soon as a ticket is created it is an open ticket. After a ticket went through the whole business process and there are no workflow activities for the ticket anymore, the ticket is a closed ticket. Closing a ticket can be done manually by an engineer or automatically by the system, e.g., after a defined waiting time after the last step of the business process.
The actions you can carry out for open tickets are described in Updating Tickets.
For closed tickets, the following applies: