Noun - A short ninja, around two feet tall, that reside in the yard in the night time. They continually stare into the windows of the residents house, as a voyeur, giggled in the background. If a person is vigilant enough, they can catch them in action. Yard Ninjas are weak against the common porcupine, but cannot be killed by one. Yard Ninjas originated around the 1300's AD, when they were discovered trampling on the grave of William Wallace
I caught me a Yard Ninja last night, bugger had 13 of my collectable Pez dispensers.... I'm gonna buy me some guard porcupines..