1. A milestone; an interesting number displayed on a web counter, such as 10000, 22222, etc.; particularly, one selected by the website owner for the purpose of giving a prize to whoever reaches it. 2. A gift or prize given to one who reaches such a milestone. 3. The system of giving gifts to those who reach web count milestones.
Also used as in attribution, as kiriban winner, kiriban number, kiriban picture, etc., or with a number indicating the kiriban, as kiriban 5000. Can also be said as kiribian.
Just means "a good place to stop" in Japanese. Mostly people use it as a way to reward their watchers.