Any support or customer service or JIRA issue has a requestor or initiator and someone who does the work to resolve the issue or ticket.
Any support or customer service ticket or JIRA issue is opened to start and closed to finished.
The person who completes the task, ticket or issue sets the ticket to resolved.
The person who wanted the work done checks the ticket or issue and sets it to closed.
If the customer or requestor does not check the work it is often set to close automatically after a certain period of time eg 3 days.
So closed is like the final agreement between requestor and resolver that yes it’s done and there is no more to do on that issue.
The flow of most tickets, tasks or issues from open to closed would be: Open > In progress > Resolved > Closed