Priority queue
A priority queue is a line where some customers are served ahead of others who arrived earlier because of an agreed rule, such as urgency, membership or a short service.
Also called: priority line, expedited queue, fast lane
In a strict line the only thing that matters is arrival time. In a priority queue, something else outranks it. A vet clinic will see an injured animal before a routine vaccination. A service counter may put a two-minute question ahead of a long form.
Priority works when the rule is reasonable and visible. People accept that an emergency goes first. They do not accept an unexplained jump, especially when the person who skipped ahead appears to be a friend of the staff.
The cost is that every jump pushes everyone else back. A small shop that gives priority to many groups ends up with no real order, and the quoted wait stops meaning anything. Keep the list of exceptions short, and say it out loud. A vet clinic, for example, might post one simple rule on the door: emergencies first, everyone else in order.
Questions
When is a priority queue appropriate?
It fits when some needs are clearly more urgent or much shorter than others, such as emergencies at a vet or quick questions at a counter, and when the rule is posted and applied the same way.