That's a good definition. It's the one that you've hunted and hunted for and when you finally get, you do a happy dance and don't stop smiling for a week.
but there is an element of it being hard to get as well. Many people here have grails that involve rare hard to find pins. It can also be a pin you desire but it is above your ability to trade. I find my grails are like that, there are some out there but I don't have traders that would get me that one in return.