tickets.is_hold records whether a ticket has been placed on hold by an agent.
The value of is_hold is 1 when the ticket is on hold, and 0 otherwise.
If you wanted your report to return only tickets that are on hold, you'd include this in your DPQL:
WHERE tickets.is_hold = 1
Note that is_hold is separate from tickets.status - a ticket that's on hold will always have a status of awaiting_agent.