In World of Warcraft, a ticket usually refers to an active Help Request to a GM for in-game support about a bug, issue or problem in-game. Most tickets do not get resolved right away, unless it is a major bug newly discovered or an obvious and traceable harassment event.
An "Open Ticket" is for an issue that has not been addressed or resolved.
See Help Request for issues that GMs should consider valid requests.
Open Ticket
You will know when you have an open ticket because a small ticket icon will appear just to the left of your Mini-Map at the top of the screen.